Time Out says
It’s free any night of the week (March–mid-November) to stroll out onto the Congress Avenue Bridge and observe the jaw-dropping spectacle that is the world’s largest urban bat population jettisoning from underneath it in cyclone-cloud formation as they fly over Lady Bird Lake eating insects. But, at some point, it’s absolutely worth the $10 to take a boat tour offered by Capital Cruises that allows you to see the sight from underneath the bridge. While you’re waiting for the bats to take flight, a knowledgeable guide will use a special light to show you the creatures in hang-mode and, for those willing to spend a little more, there are private rides available with customized options including dinner and cocktails.
208 Barton Springs Rd
|Opening hours:||Mon-Fri 10am-2am; Sat, Sun 9am-2am|