The first railroad tunnel in Texas was the Fredericksburg and Northern. After the railroad was abandoned it was turned into a bat habitat. It is over 900 feet long and is now a state park. I stopped by in the off season and the sign said $5 per person (wow). The tunnel is closed in the off season so check with state website for info. Half a mile east of the Fredericksburg city limits along U.S. 290, look for the brown TxDOT highway sign that says "Old Tunnel Wildlife Area." Go south 10.5 miles on the "Old San Antonio Road." The WMA is on the left. The phone number gives info on the bat cave.