The Musée de la Mer, housed in a circular 1930s Art Deco building directly above the Côte des Basques beach, is one of the better small aquariums in France. The main focus is the marine life of the Bay of Biscay — Atlantic sharks, rays, sea bass, moray eels, and a large circular tank containing species typical of the local coast. The seal feeding shows are the crowd-pleaser. There are also tanks of tropical species and exhibits on the whale-hunting past of the Basque coast.
The building's position and architecture make it worth a visit even if aquariums are not normally your thing — the terraces above the tanks look directly out onto the Atlantic, and the views down the Côte des Basques beach are excellent. Combined tickets are sometimes available with the Cité de l'Océan science museum further inland.