Seattle Aquarium

Located along the waterfront behind Pike Place Market, the Seattle Aquarium is actually a collection of buildings built on a pier over Puget Sound. Inside the main entry building, they have a typical selection of tropical and semi-tropical acquatic creatures. (An octopus, jellyfish, and a number of interesting-looking fish in ~30 or so tanks)

An outdoor area and the second building host the aquarium's pacific-northwest related exhibits. Those exhibits include birds, seals, otters, and the like outdoors, and an underwater section devoted to fish native to the Puget Sound. An afternoon-visit sort of length, it's also a popular spot for school trips.