The centrepiece is a 200,000-gallon Giant Ocean Tank in the middle of the building, ringed by a spiralling ramp that takes visitors from the tropical surface down past hawksbill turtles, sand-tiger sharks, and a thousand other Caribbean reef fish. Divers feed the residents several times a day, communicating with the crowd through underwater mics.
Outside the tank, the harbour seals splash in an open-air pool that anyone can watch for free from the harbourwalk. The penguin colony — African penguins, southern rockhoppers, little blues — is the loudest exhibit. The IMAX cinema next door shows ocean documentaries on a six-storey screen.
Whale-watching boats run from the dock in summer; the four-hour trips out to Stellwagen Bank are one of the best wildlife experiences anywhere on the east coast. Aquarium admission is steep — go on weekdays if you can to avoid the school groups that fill the place from 10 am.