Entrance to the Hospital de Sant Pau | Photo: Tom Walton
The Hospital de Sant Pau (or the Hospital de la Santa Creu i Sant Pau, to give it its full name) is just a couple of blocks up from the Sagrada Familia.
Architect Domènech i Montaner (1850-1923) designed it to create the sort of pleasant surroundings that would aid its patients' recovery, with a series of tunnels hidden away below ground linking the different pavillions and providing the hospital with its services.
If you're going to visit the Sagrada Familia, do go to the Hospital de Sant Pau, too. It's well worth it.