Lisbon's Oceanarium is the largest indoor aquarium in Europe. With over 450 species of fish, marine mammals and birds, it is certainly worth several hours of visitors' time. One unique resident in the Oceanarium is a sunfish (shown here), a species rarely kept in aquariums because it is so difficult to care for. The main tank features a plethora of aquarium standards: sharks, eels, rays and schooling fish. It is perhaps fitting that, given Portugal's long history as a seafaring nation, the exhibits cover every major ocean on the globe, with an Arctic exhibit, an Atlantic Ocean tank, a tropical Indian Ocean habitat, and tanks housing species from the Pacific's temperate waters.