Old Tunnel State Park: Texas’ Smallest Park with the Biggest Nightly Show
Nestled deep within the rugged and scenic Texas Hill Country lies a hidden treasure that boasts a title quite unlike any other. Welcome to Old Tunnel State Park, officially recognized as the smallest state park in Texas. But do not let its compact size of just 16.1 acres fool you. Located approximately 14 miles south of the charming town of Fredericksburg and about 60 miles northwest of San Antonio, this miniature wilderness refuge delivers an oversized, breathtaking experience.
The park’s centerpiece is a colossal, abandoned railroad tunnel that has been reclaimed by nature. It now serves as the seasonal home to millions of bats. Whether you are a wildlife enthusiast, a history buff, or just looking for the perfect family-friendly evening outing, Old Tunnel State Park offers a unique blend of natural wonder and historical intrigue.
Key Takeaways
- Old Tunnel State Park is the smallest state park in Texas at just 16.1 acres. It is located 14 miles south of Fredericksburg and 60 miles northwest of San Antonio.
- The park’s abandoned 920-foot railroad tunnel houses up to 3 million Mexican free-tailed bats and 3,000 cave myotis bats seasonally from May through October. Close to 100 workers hand-dug the tunnel through Glen Rose limestone in 1913.
- The tunnel functions as a pseudo-maternity colony. Female bats temporarily reside but do not give birth here. They leave the tunnel to give birth, then return. This causes population fluctuations with peak numbers occurring in August and September when mothers return with newly flying juveniles.
- Bat viewing requires advance ticket purchases online or by phone. Upper viewing area access costs $2 per person, seven nights weekly. Lower viewing area access costs $5 per person, Thursday through Sunday, with a 70-person capacity limit.
- Mexican free-tailed bats can reach horizontal speeds exceeding 99 mph and fly at altitudes of 10,800 feet. This makes them among the fastest and highest-flying animals, while consuming their entire body weight in insects nightly.
A Journey Through Time: The History of the Tunnel
Before it became a wildlife sanctuary, the site of Old Tunnel State Park was a bustling hub of human engineering and ambition. In the mid-1800s, as European settlers expanded into the Texas Hill Country, they desperately needed a reliable transportation and trade route to connect the farmers of Fredericksburg to the thriving merchants in San Antonio. However, a massive limestone ridge known locally as the “Big Hill” stood squarely in their way. A tunnel must be built to bring goods back and forth from Fredericksburg and San Antonio. Steam trains in that era could not climb such a steep grade. Therefore, the tunnel became necessary.
For decades, the sheer cost of breaching the Big Hill thwarted construction plans. It wasn’t until 1913 that residents finally raised enough funds to tackle the monumental project. A crew of roughly 100 workers, primarily local laborers of German descent, undertook the grueling task of digging through the solid Glen Rose limestone. Remarkably, workers bored out most of the tunnel entirely by hand.
Tunnel Specifications
The finished product was an engineering marvel with the following specifications:
| Specification | Measurement | Modern Comparison |
| Tunnel Length | 920 feet | 2.5 football fields |
| Height | 20 feet (6 meters) | Two-story building |
| Width | 16 feet (5 meters) | Single traffic lane |
| Labor Force | 100 workers | Primarily of German descent |
| Construction Method | Hand-dug through limestone | No mechanical equipment |
The Fredericksburg and Northern Railway operated through this passage for several decades. Despite its popularity and utility to the locals, the railway was never truly profitable. As the United States entered World War II in 1941 and 1942, military officials deemed the rail line non-essential. They dismantled the railroad, repurposing the iron rails and wooden ties for the military effort.
Once the trains stopped passing through, the quiet, dark, and cool environment attracted a brand-new set of residents: millions of bats. To protect this unique ecological site, the Texas Parks and Wildlife Department (TPWD) acquired the property in 1991. It officially turned management over to the State Parks Division in 2012.
The Main Attraction: A Spectacle of Millions
Today, the undisputed star of Old Tunnel State Park is its massive bat colony. Every year, between May and October, the tunnel becomes a seasonal refuge for up to 3 million Mexican free-tailed bats and approximately 3,000 cave myotis bats.
Interestingly, this is what wildlife biologists call a “pseudo-maternity colony”. Pregnant and lactating female bats utilize the tunnel during the summer, but they do not actually give birth inside it. Instead, they temporarily relocate to nearby caves or bridges that offer more stable temperature and humidity levels for their pups. Because of this fascinating ecological behavior, the population at Old Tunnel fluctuates significantly throughout the season.
In June, you might see a dip in numbers as females leave to deliver their pups. By early August, however, the mothers return alongside their newly flying juveniles. Thus, the tunnel’s population swells to its absolute peak in August and September.
When the weather begins to cool down in late October, the bats migrate further south into Mexico for the winter. This leaves the tunnel mostly empty until the cycle begins the following spring anew.
| Time Period | Population Level | Bat Activity |
| May – Early June | High (2-3 million) | Pregnant females arrive |
| Mid to Late June | Moderate (1-2 million) | Females relocate to birth caves/bridges |
| July | Moderate-High (2 million) | Mothers begin returning |
| August – September | Peak (3+ million) | Juveniles join the colony |
| October – April | Minimal to None | Migration to Mexico |
Experiencing the Bat Emergence: Viewing Areas and Tips
As the sun begins to set over the Texas Hill Country, the magic happens. Millions of bats awaken, creating a sound akin to rushing water as tiny wings flap together, even stirring a light breeze. They spiral out of the tunnel’s entrance in a massive, smoky column, gaining altitude to spread out and hunt for insects overnight.
To witness this awe-inspiring natural display, you have two primary options. Both options require an entrance fee for bat viewing tickets if you wish to stay past 5:00 p.m. during bat season (May 1 through October 31). It is critical to note that tickets are not sold on-site and must be purchased online or by phone in advance. Cell service is notoriously spotty in the canyon. Therefore, print your tickets or take a screenshot of your ticket before you arrive.
Interesting Facts about Bats
Bats really are amazing mammals! Here are eight interesting facts about Mexican free-tailed bats (Tadarida brasiliensis):
- They are incredibly fast and high flyers. Mexican free-tailed bats have been claimed to reach the fastest horizontal speed of any animal. They can reach top ground speeds exceeding 99 mph (160 km/h).
- These high-flying creatures ascend to impressive heights. Furthermore, they fly higher than any other bat, reaching altitudes of around 10,800 feet (3,300 meters).
- They use acoustic sabotage to steal food. While hunting for insects, these bats can emit specific ultrasonic vocalizations designed to “jam” the echolocation calls of rival bats. This reduces the rival bat’s chances of catching a moth, allowing the jamming bat to swoop in and catch the prey instead.
- Their toes glow under UV light. They possess large feet with distinct, long white bristles on the outer toes and the edge of their tail membrane. For reasons that remain unknown to scientists, these bristles are photoluminescent and glow under ultraviolet light.
- They have built-in defenses against toxic ammonia. Because these bats roost in massive, concentrated colonies, their caves accumulate thousands of tons of guano and urine, generating highly toxic levels of airborne ammonia. The bats survive this environment through a genetic adaptation that increases the CO2 and protein in their respiratory mucus and blood plasma, successfully buffering and filtering the ammonia before it poisons their blood.
- Their fur has natural antimicrobial properties. The pelage (fur) of Mexican free-tailed bats contains a chemical called nonanal. This chemical acts as an antimicrobial agent that inhibits the growth of ringworm-causing fungi and common skin-disease microbes like Staphylococcus aureus.
- They inadvertently share nursing duties. Mother bats give birth to a single pup. They leave them clustered together in massive “creches” while they go out to hunt. Although mothers use unique scents and vocalizations to identify their own babies upon return, the overwhelming size of the colonies means they aren’t always accurate; roughly 17% of mothers end up nursing pups that are not their own.
- They are champions of agricultural pest control. A single Mexican free-tailed bat can eat its entire body weight in insects in a single night. The colony at Bracken Cave in Texas is the largest bat colony in the world, with over 15 million bats. Thus, no surprise that these bats eat an estimated 100 tons of crop pests, such as corn earworm moths, every single summer night.
- Predators of the Mexican Free-tailed Bat include aerial predators such as hawks, falcons, and owls. Ground predators include mammals such as Racoons, skunks, and opossums. Reptilian predators include snakes like the eastern coachwhip and the eastern coral snake.
Adaptation
Bats are an incredible mammal that has adapted over the years:
| Adaption Type | Capability | Survival Benefit |
|---|---|---|
| Flight Speed | 99+ mph horizontal speed | Predator evasion and extended hunting range |
| Attitude Capability | 10,800 feet maximum | Access to high-altitude insect populations |
| Ammonia Tolerance | Blood chemistry buffering system | Survival in high-density toxic roosts |
| Antimicrobial Fur | Nonanal chemical secretion | Disease resistance in crowded colonies |
| Echolocation Jamming | Ultrasonic interference calls | Competitive advantage in prey capture |
The Bat Viewing Areas
The Upper Viewing Area:
The upper observation deck features bleacher seating and is open seven nights a week from May to October. It’s located right adjacent to the parking lot. Admission here is highly affordable at just $2 per person, regardless of age. From this vantage point, you can watch the bats rise out of the deep canyon and fill the twilight sky. It is recommended to bring binoculars to the park, especially if in the Upper Viewing Area.
The Lower Viewing Area:
For a more intimate, up-close encounter, the lower viewing area sits much closer to the tunnel’s entrance. This section is only open on Thursday through Sunday evenings and costs $5 per person. The bats are highly sensitive to noise and disturbance. This area has a strict capacity limit of 70 people, and children under 4 are not permitted.
| Feature | Upper Viewing Area | Lower Viewing Area |
| Cost | $2 per person | $5 per person |
| Open Days | 7 nights per week | Thursday-Sunday Only |
| Capacity | Unlimited | 70 people maximum |
| Age Restriction | All ages welcome | 4 years or older only |
| Viewing Distance | Canyon Overview (bring binoculars) | Tunnel entrance proximity |
We reserved the lower viewing area which gives you a close-up view of the bat emergence. The bats actually came out early, before the park ranger came down to give the informational portion of the viewing. It was thought someone had popped some firecrackers at the other entrance to the tunnel and spooked the bats into leaving early.
Educational Program
During the emergence, park rangers provide excellent educational programs focusing on the life history and ecology of the Mexican free-tailed bat, typically starting 30 minutes to an hour before the flight. The rangers use this time to dispel widespread myths about bats and to educate visitors on the immense ecological benefits these insect-hunting mammals provide.
Activities In and Around the Park
While the evening bat flight is the park’s main event, Old Tunnel State Park and its immediate surroundings offer several other excellent activities to round out your visit.
Dining at Alamo Spring Cafe
One of the absolute best parts of visiting Old Tunnel State Park is its proximity to a local culinary legend. Right next door to the park sits the Alamo Springs Café, a beloved, family-friendly Hill Country staple known for its massive, mouth-watering burgers and casual outdoor seating. Combining an early dinner at the café with a short walk over to the state park for the sunset bat flight makes for a flawlessly executed, stress-free evening. We had a fabulous meal listening to live music, then walked over to the park. You can walk from the park’s parking lot.
Hiking the Nature Trail
If you arrive before 5:00 p.m., the park is free to enter, and you can explore the Old Tunnel Nature Trail. The hiking trail, which spans roughly a half-mile to three-quarters of a mile round-trip, is open year-round from sunrise to 5:00 p.m. The path winds through beautiful Hill Country woodlands comprised of live oak, Ashe juniper, black walnut, and escarpment black cherry. Keep an eye on the canopy, as the area is fantastic for birdwatching. You might spot a painted bunting, Carolina chickadee, yellow-billed cuckoo, or various raptors soaring gracefully over the canyon. As you hike, interpretive kiosks offer insights into the region’s wildlife, the decomposition of materials, and the engineering history.
Picnic Tables
Bring a snack and utilize the picnic tables. There are only a few, so first-come, first-served.
Whether staying in Fredericksburg or a campsite, this area is well worth exploring. We drove around, just turning onto side roads, looking around. We got to see real, authentic Texas.
Exploring the Surrounding Hill Country
Because Old Tunnel lacks camping and overnight facilities, it makes a perfect day trip from nearby hubs. The park is only 14 miles from Fredericksburg, renowned for its German heritage, boutique shopping, and extensive wineries. If you are an outdoor enthusiast looking to pitch a tent, you can easily combine your Old Tunnel visit with a stay at nearby state parks like Enchanted Rock State Natural Area, Blanco State Park, or Guadalupe River State Park.
Know Before You Go: Rules and Accessibility
Park Rules
Because Old Tunnel State Park is primarily a wildlife management area designed to protect a sensitive bat colony, the Texas Parks and Wildlife Department enforces strict rules to ensure the animals are not disturbed.
- Pets are entirely prohibited in the park, so you must leave your furry companions at home.
- Furthermore, to protect the natural environment and the bats’ health, smoking and alcohol use are strictly forbidden.
- Visitors are also urged to stay on designated trails, must never approach the tunnel entrance, and are encouraged not to make loud noises.
- Lastly, there is no potable water available on-site, so it is highly recommended that you bring your own drinking water.
| Restriction Category | Policy | Reason |
| Pets | Entirely prohibited | Wildlife disturbance prevention |
| Smoking/Alcohol | Strictly forbidden | Environmental and bat health protection |
| Trail Usage | Designated trails only | Habitat preservation |
| Noise Levels | Keep volumes low | Sensitive bat colony protection |
| Water Availability | None on-site – bring your own. | No facilities available |
Accessibility
From an accessibility standpoint, TPWD has made great strides in accommodating visitors. The lower viewing area, along with the trail leading down to it, currently meets ADA accessibility guidelines. The park provides accessible parking stalls and paved surfaces at the parking lot and entrance. While some natural terrain elements—such as the crushed-stone outdoor recreation routes and picnic areas—require ongoing maintenance, park staff occasionally allow wheelchair users to park much closer to the lower viewing area so everyone can enjoy the incredible bat emergence.
How to Get There
The State Park is located approximately 13.7 miles from Fredericksburg, TX, on the old San Antonio Road. It will take you about 23 to 25 minutes. It is a beautiful drive to the park. We saw several deer along the way.
More Resources
An excellent resource for additional, up-to-date information can be found on the old tunnel Facebook page at Old Tunnel State Park – Texas Parks and Wildlife Facebook page. The site is managed by the Texas Parks and Wildlife Department (TPWD).
Most Important Insights to Remember
- Advance ticket purchases are mandatory for bat viewing because tickets are not sold on-site and cell service is unreliable in the canyon, so purchases must be made online or by phone, with printed or screenshot confirmation before arrival.
- Peak bat populations occur in August and September when mothers return with newly flying juveniles after giving birth in nearby caves, swelling the colony to over 3 million individuals compared to lower numbers in June when females temporarily relocate for birthing.
- The 1913 hand-dug tunnel represents extraordinary engineering, with 100 workers manually excavating 920 feet through solid Glen Rose limestone to create a passage that served as a railway until 1942, after which it was repurposed as critical bat habitat.
- Mexican free-tailed bats possess unique biological adaptations, including blood chemistry modifications that neutralize toxic ammonia, antimicrobial fur compounds, echolocation-jamming capabilities, and unexplained photoluminescent toe bristles visible under UV light.
- Combining Alamo Springs Café with the bat viewing creates an optimal evening experience by providing high-quality dining and live music immediately adjacent to the park, eliminating the need to drive between locations, and allowing visitors to walk directly from lunch/dinner to the emergence program.
Conclusion
Old Tunnel State Park might be the smallest state park in Texas, but the memories you make there will be anything but small. The fascinating view of a massive, hand-dug railroad tunnel and the millions of tiny, fluttering bats that now call it home serves as a beautiful reminder of how nature reclaims and thrives in human-made spaces. Between the educational ranger programs, the stunning Hill Country hikes, a fantastic burger next door, and a sunset spectacle that truly rivals any fireworks display, a trip to Old Tunnel State Park is an absolute must-do for any Texas travel bucket list. Book your tickets online, pack your binoculars, and prepare to have your mind blown by the night flyers of the Texas Hill Country!
Make sure you check out all our other posts on the Texas Hill Country. This includes posts covering the Enchanted Rock State Natural Area, the Fredericksburg Winery, Hike the Cross Mountain Trail, Fun Things to Do in New Braunfels, TX, Krause’s Café and Biergarten (New Braunfels, Texas), McKinney Falls State Park, and several others. Feel free to share the post and subscribe!
MINI GLOSSARY
Pseudo-Maternity Colony: A seasonal bat roosting site where pregnant and lactating female bats temporarily reside but do not give birth, instead relocating to caves or bridges with more stable temperature and humidity for delivering pups.
Mexican Free-Tailed Bat (Tadarida brasiliensis): A medium-sized insectivorous bat species capable of reaching speeds exceeding 99 mph and altitudes of 10,800 feet, known for forming massive colonies of millions of individuals in caves, bridges, and abandoned structures.
Echolocation Jamming: A competitive hunting strategy where bats emit specific ultrasonic vocalizations designed to interfere with the echolocation calls of rival bats, reducing their ability to capture prey and allowing the jamming bat to intercept insects.
Glen Rose Limestone: A thick formation of hard limestone rock found in the Texas Hill Country, formed during the Cretaceous period approximately 100 million years ago, through which the Old Tunnel railroad passage was hand-excavated.
Photoluminescence: The emission of light from a substance after it has absorbed photons or electromagnetic radiation, observed in Mexican free-tailed bat toe bristles when exposed to ultraviolet light, though the biological purpose remains scientifically unknown.
Frequently Asked Questions
What happens if it rains on the day of my reserved bat viewing?
Bats typically do not emerge during heavy rain or storms because flying insects remain grounded in wet conditions, eliminating the bats’ food source. Drizzle may not prevent emergence, but bats often delay their exit or emerge in smaller numbers. Texas Parks and Wildlife does not issue refunds for weather-related cancellations, so check the forecast carefully and consider rescheduling if severe weather is predicted.
Can I visit Old Tunnel State Park during the winter months when bats are absent?
Yes, the park remains open year-round for hiking from sunrise to 5:00 p.m., and the entrance is free during daylight hours outside of bat season (November through April). The nature trail provides excellent birdwatching opportunities and interpretive displays on the tunnel’s railroad history, though the bat viewing areas are closed and no evening programs are offered during the winter months.
Is this a good place to bring kids?
Absolutely, it is a fantastic, highly memorable place to bring kids. The hiking trail to the lower viewing area and beyond is a very manageable 0.5-mile loop, making it perfect for smaller legs. Park volunteers are often on-site to teach kids about the bats and the history of the old railroad. If you want to get a ticket in the lower viewing area, the child must be 4 years old or older due to the bats’ sensitive hearing. It can make them emerge prematurely. There were kids all over the place on the afternoon we went to observe the bats coming out of the tunnel.
Are there any nearby accommodations specifically recommended for multi-day Hill Country exploration?
Fredericksburg offers numerous bed-and-breakfasts, hotels, and vacation rentals within 20 minutes of the park, making it an ideal base for combining a visit to Old Tunnel with visits to Enchanted Rock State Natural Area, Lyndon B. Johnson State Park, and the area’s many wineries. For camping enthusiasts, Enchanted Rock is 30 minutes north, while Guadalupe River State Park is 45 minutes southeast, both offering developed campsites with more extensive trail systems.
How early should I purchase tickets for peak-season weekends?
Lower-viewing-area tickets for Friday through Sunday evenings in August and September frequently sell out 2-3 weeks in advance due to the 70-person capacity limit. Upper viewing area tickets rarely sell out due to unlimited capacity, but purchasing tickets at least one week in advance ensures you won’t be disappointed, especially during holiday weekends or special events in Fredericksburg.
What photography equipment works best for capturing the bat emergence?
The evening emergence occurs during low-light conditions, requiring cameras capable of high ISO settings (1600-3200) and fast shutter speeds (1/500 second or faster) to freeze bat motion. Telephoto lenses in the 200-400mm range work well from the upper viewing area, while the lower viewing area accommodates wider shots with 24-70mm lenses. Tripods are permitted but must not obstruct walkways or other visitors’ views, and flash photography is strictly prohibited as it disturbs the bats.
