Belém Tower

A UNESCO site that started as a lighthouse and customs house, built to show off Portugal's wealth during the Age of Discovery. King João II wanted a defense system for Lisbon's port, but it was his successor Manuel I who got it built in 1519. Standing there like a chess piece in the Tagus river, it's covered in stone ropes, rhinoceros gargoyles, and other exotic carvings - each telling tales of Portugal's maritime adventures. The tower has been everything from a lighthouse to a political prison, where they kept the prisoners in a tiny dungeon that would flood at high tide. (Tip: go early morning on weekdays to avoid tourist crowds, and don't miss the dragon sculptures on the facade - they were inspired by Saint Vincent, Lisbon's patron saint.)