The wildlife management area is open nightly from May - Oct. for a spectacular emergence of up to 3 million Mexican free-tailed bats from an abandoned tunnel of the old San Antonio, Fredericksburg and Northern Railway Co. that operated from 1913 to 1942. The upper viewing deck is free. Every Thurs. - Sun. guided tours are given to the lower observation deck with a fee. Reservations are not accepted. Group tours by reservation only Mon. - Wed. Call for information and reservation for the tour.