Old Tunnel State Park: A Texas Hill Country Landmark with a Remarkable Bat Colony

Old Tunnel State Park is the smallest state park in Texas at 16.1 acres. It sits in the Hill Country near Fredericksburg and is built around a historic railroad tunnel once used by the San Antonio, Fredericksburg and Northern Railway beginning in 1913. The Fredericksburg and Northern Railway later operated the line until service ended in the early 1940s. The tunnel, carved through limestone, is roughly 920 feet long and today serves as a protected seasonal roost for large bat colonies.

A Seasonal Home for Bats

From spring through fall, the tunnel hosts an impressive number of bats. The population includes as many as three million Mexican free-tailed bats and several thousand cave myotis bats. These colonies gather in the tunnel during the warmer months before migrating south for winter. Visitors can watch the evening emergence during the season, though access to designated viewing areas typically requires a permit or ticket due to the park’s small size and wildlife protections.

History of the Railroad Tunnel

Construction on the tunnel began in the early twentieth century to support a regional railway linking Fredericksburg with the larger rail network toward San Antonio. Trains traveled through the limestone passage for several decades, carrying freight and passengers across the Hill Country. When the railway ceased operations around 1942, the tracks were removed and the tunnel was left unused. Over time, it became a natural roost for bats, and the area eventually gained protection as a wildlife habitat and later as a Texas state park.

Nature Trail and Daytime Activities

Old Tunnel State Park includes a short nature trail measuring less than half a mile. The trail is open during daytime hours and provides opportunities for bird-watching, wildlife observation, and views of native Hill Country plants. Because the park is small and focused on habitat preservation, daytime visitation is limited to low-impact activities, while evening access during bat season follows specific rules to protect both visitors and the wildlife.