The Edwards Aquifer, Austin's main source of water, is fed by a variety of underground creeks filtered through a large layer of limestone. You'll feel as though you're entering one of this vast ecosystem's sinkholes when you walk into the dimly lit enclosure -- formerly the bathhouse at Barton Springs pool -- where a variety of interactive displays grab kids' attention. Young visitors can make it rain on the city, identify water bugs, or peer through a periscope at swimmers. Although the focus is on the evils of pollution, the agenda is by no means heavy-handed.