Lisbon's Oceanarium is one of the world's largest aquariums. Designed by American architect Peter Chermeyeff, it rises from the river and is reached by a footbridge.
It is a deep-sea diving experience without any of the risks, with about 25,000 fish, seabirds, and mammals in an enormous central tank that is the size of four Olympic-sized swimming pools.
Visitors can look into it from different levels for close-ups of the various creatures, including different species of sharks.
But it's the design rather than the size that makes it outstanding.
It is the first aquarium ever to incorporate world ocean habitats within a single environment, with impressive recreations of various ocean ecosystems, the Antarctic tank containing penguins, and the Pacific tank with otters playing in rock pools.
They are all separated from the main tank by invisible acrylic walls, giving the impression that all the creatures are swimming in the same space.