An abandoned railroad tunnel in the Fredericksburg area has some flying inhabitants -- an estimated three million of them.
The Mexican free-tailed bats live in what's known as "The Big Hill."
The nightly show runs May through October as the bats depart each evening to devour tons of insects.
The 16-acre Old Tunnel Wildlife Management Area has become the most popular of the more than four dozen such areas managed by the Texas Parks and Wildlife Department.
Officials said more than 5,000 people visited the site about 65 miles west of Austin in July.
Wildlife biologist Nyta Hensley said the bats "have this air of mystery" about them because they're only out at night.
The tunnel became home to the bats some time after the San Antonio, Fredericksburg & Northern Railroad abandoned its track nearly 30 years ago.