It all started with the house for the Hieronymite monks, a hermitage that was founded by Prince Henry the Navigator at about 1450, where Vasco da Gama and his men spent the night in prayer before departing for India in 1497. The existing structure was started on the orders of King Manuel I to commemorate their successful return, whose construction began in 1502 and took 50 years to complete. Surprisingly the building withstood the great earthquake of 1755 without too much damage.
This monastery can be considered one of the most prominent monuments in Lisbon and is certainly one of the most successful achievements of the Manueline style. In 1983 it was classified by the UNESCO, with nearby Belem Tower, as a World Heritage Site.
The building is huge, these are just partial views.