Zaragoza's River Aquarium was built for Expo 2008 and keeps an unusual focus: rivers rather than seas. Its tanks and displays compare freshwater ecosystems from the Ebro to the Nile, Mekong, Amazon, Murray-Darling, and other great river systems.
That theme makes it more interesting than a generic aquarium, especially in a city shaped so strongly by the Ebro. It is a good family stop and a useful companion to walks along the riverfront and the Expo-era public spaces.