Waugh Drive Bat Colony
Each night during Houston's sultry summer months, during that magical moment between sunset and dusk, you can head to Waugh Drive Bridge and see over 250,000 Mexican Free-Tail bats emerge from the caverns. This incredible sight attracts quite the crowd each night (unless the weather prevents so, of course), both locals and tourists awed by the event.
The general suggestion is to get to the bridge 15-30 minutes before sunset for the best viewing chances. During the months of June and July, you can see up to 20,000 bat pups, though the peak viewing season, in general, is during August and September.
It won't be hard to find the bridge, the almost mile-long connector located directly over Buffalo Bayou. Right across from the spot you will see the American General Tower, also very hard to miss (the very tall building with the American flag).
If interested, your group can take a Waugh Drive Bat Colony Pontoon Boat tour, offered the 2nd and 4th Fridays April through September. The ride lasts about an hour and a half and not only gets you close to the colonies cave quarters, but also informs you on the bats, their part in the local eco-system, and colony habits in general. This tour will run you about $30 for adults, and children under 4 cannot participate.