Barcelona. Spectacular, beautiful, and full of Gaudi. If you want a general overview, just choose the first file. If you want to see Barcelona in detail, try the others, but be warned, there are a lot of photos.
Casa Batllo was built in 1877 and remodelled in 1905-1907. Gaudi has managed to design a building with virtually no straight lines whatever.
Casa Mila, also known as La Pedrera, is just up the road from Casa Batllo. Another Gaudi masterpiece, it has been restored and has a large number of exhibits explaining Gaudi and his work on this and other buildings.
Parc Guell is another of Gaudi's impressive works. A failed attempt at a housing estate, it was taken over by the city and is now a park.
Las Ramblas, the place to stroll in Barcelona. Plenty of street theatre, and people-watching, and the markets are full of fresh fruit, vegetables, and seafood.
And the unfinished masterpiece, Sagrada Familia.