Barcelona is capital of Catalonia and world-famous for soccer and architecture. You must visit the cathedral Sagrada Familia, designed by Gaudi, that has been under construction since 1883. Camp Nou, where FC Barcelona resides, is an experience of a different kind.
Madrid, capital of Spain and home of the royal family. The city center with great architecture is amazingly small, with nice places to enjoy local food and wines and very walkable.
Seville is the capital of the Andalusian region that also includes Malaga and Granada. It is very Spanish here with historical buildings, Flamenco Music & Dance, horses, Paella and Sangria. Note that it can be really hot (40°C and more) in Summer...
Pamplona is best-known for its annual "running with the bulls"... Yes, these are real bulls and it is dangerous! Only the very sporty ones that have something to prove, should try this...
San Sebastian is a superb beach location just west of the Pyrenees with excellent food (tapas). It should be on everyone's itinerary.
Cadiz is one of the oldest cities in Europe. It's location is quite unique, since it is surrounded almost completely by water (similar to Venice). James Bond used the city to resemble Cuba.
Jerez is known mainly for two things: 1) the bodegas for the finest Sherries and 2) the Equestrian School for ultimate horse back riding demonstrations. Add to this great weather, some flamenco and lots of orange trees and then you know something about Jerez de la Frontera.
Málaga is an important tourist destination, known as "the capital of the Costa del Sol". An estimated 6 million tourists visit the city each year, who usually visit the birthplace of Pablo Picasso.