The summer home of the world's largest bat colony — an estimated 15 to 20 million Mexican free-tailed bats (Tadarida brasiliensis) who roost in this limestone cave from March to October, giving birth to their pups in late June. The nightly emergence, beginning around dusk, is a spectacular natural phenomenon: a continuous black column of bats pouring from the cave entrance for two to three hours.
Access is by reservation only through Bat Conservation International, which owns and manages the property. Evening emergence tours run from late May through August and must be booked well in advance. The cave is about 20 miles north of downtown San Antonio. Dress in layers — cave air is cool even in summer.