Oceanário de Lisboa
Built for Expo '98 on land that was once industrial wasteland, this is Europe's largest indoor aquarium. The building looks like a floating aircraft carrier, designed to make you feel like you're walking on water. The central tank is so big it holds 5 million liters of seawater - that's like 2 Olympic swimming pools! They change the water so slowly (to avoid shocking the fish) that it takes a month to do a complete renewal. Each corner represents a different ocean, but they're all connected - just like in real life. (Tip: book the 'Backstage' tour to see how they feed the sharks and what goes on behind those massive tanks.)