Built in 1515 as a fortress to guard the entrance to Lisbon's harbor, the Belem Tower was the starting point for many of the voyages of discovery, and for the sailors it was the last sight of their homeland. It’s a pretty iconic symbol of Lisbon and Portugal. It's a monument to Portugal's Age of Discovery and UNESCO has listed it as a World Heritage monument. When in the Belém area - make sure to stop and admire this icon - although actually going inside might not be essential.