Monastery of the Hieronymites and Tower of Belém in Lisbon

Standing at the entrance to Lisbon harbour, the Monastery of the Hieronymites – construction of which began in 1502 – exemplifies Portuguese art at its best. The nearby Tower of Belém, built to commemorate Vasco da Gama's expedition, is a reminder of the great maritime discoveries that laid the foundations of the modern world. [source]

I haven’t been here (yet).