A hospital since 1401
In 1401 six small medieval hospitals merged into the Hospital de la Santa Creu. Five centuries later, the city needed something bigger, and the banker Pau Gil's legacy paid for this one.
Built between 1901 and 1930 by Lluís Domènech i Montaner, the Hospital de Sant Pau treated patients until 2009. Its 12 Modernista pavilions, joined by underground tunnels, form the largest Art Nouveau complex in the world.

In 1401 six small medieval hospitals merged into the Hospital de la Santa Creu. Five centuries later, the city needed something bigger, and the banker Pau Gil's legacy paid for this one.
Instead of one big block, Domènech i Montaner designed separate pavilions surrounded by gardens, with light and fresh air, joined by underground galleries for moving patients.
When a new hospital opened next door in 2009, the old pavilions were restored. They reopened in 2014 as a cultural centre and offices for international organisations.
Not the Modernista pavilions. The hospital moved to a new building next door in 2009; the old complex reopened in 2014 as a cultural centre you can visit.
Lluís Domènech i Montaner, who also built the Palau de la Música Catalana.
If you like Gaudí, yes: it's the largest Art Nouveau complex in the world and far less crowded than the Sagrada Família.