Clear, acrylic underwater tunnels give visitors a diver's-eye view of the Bay, while moving walkways take you through 300ft (91m) of water, past more than 23,000 aquatic creatures. Upstairs, there are several touch-tide pools with urchins and bat rays. If you've got time, combine your visit with an island hop or Bay cruise. Blue & Gold Fleet (705 5555, www.blueandgoldfleet.com) offers hour-long Bay cruises, as well as trips to Angel Island, departing from Pier 39. Alcatraz Island Cruises (981 7625, www.alcatrazcruises.com) does two-and-a-half-hour and half-day tours of Alcatraz and Angel Islands, departing from nearby Pier 33.