Antoni Gaudi was an architect. Much of his work can be seen in Barcelona. The top left photo on the postcard is his magnum opus the Sagrada Familia. A Roman Catholic church in Barcelona. It is a Unesco World Heritage Site. In November of 2010 it was consecrated and proclaimed a minor basilica by Pope Benedict XVI.
The bottom left photo is the Park Guell. It is situated on the hill of El Carmel in Barcelona. It is also an Unesco World Heritage Site.
The bottom right photo is Casa Batllo. The local name for it is House of Bones.
The top right photo is Casa Mila better known as La Pedrera (The Quarry) It was named a Unesco World Heritage site in 1984.