Bats!

"The world's largest urban bat population" lives under a bridge in downtown Austin, Texas. They've become a big tourist attraction and the Austin American Statesman newspaper has a slick, simple Flash presentation on its Web site explaining the phenomenon.

The "bat viewing times" phone number up in the cornor is a nice idea that makes it possible for viewers to take the next step. It's sponsored by a "bat boat tour" company, but eventually tells you just when to stop by the bridge to see the little guys take flight.