The smallest state park in Texas is sixteen acres of hillside southeast of Fredericksburg with an abandoned railroad tunnel in it. The San Antonio and Aransas Pass Railway bored the tunnel in 1913, gave up on the line in 1942, and sealed the ends. Sometime after that, the bats moved in.
Up to three million Mexican free-tailed bats now summer at Old Tunnel State Park, along with a few thousand cave myotis. From May through October they come out at dusk in a column that takes twenty minutes to clear the tunnel mouth and sounds, from the lower viewing area, like running water.
August and September are the peak
The colony is not the same size all summer. The females arrive in spring and then leave to give birth, so June can be thin. By early August the mothers and that year’s juveniles are back, and the numbers climb through mid-August and hold into September. If you only get one shot at this, take it now.
Tickets are required after 5 p.m. from May 1 through October 31, and none are sold at the gate. Buy them before you drive out.
Upper deck or lower deck
There are two ways to watch. The upper viewing area is free, first-come, and looks down on the flight from above. The lower viewing area costs a few dollars, takes a small group, comes with a ranger talk, and puts you close enough to hear wings. Both are good. The lower one is the one people remember.
- Buy tickets in advance — the park does not sell them on site.
- Emergence time drifts through the season; the park runs an information line for same-day timing.
- Arrive with light to spare. The walk down to the lower deck takes a few minutes.
- Bring bug spray, water, and something to sit on. You will be still for an hour.
- No flash, no white light, no drones. Red light only, if you need any.
Old Tunnel sits about ten miles off US‑290 on Old San Antonio Road, so you can spend the afternoon on the wine road and still make dusk comfortably. Fredericksburg is twenty minutes north for dinner afterward, though everything out here closes earlier than you think.
