Spain is one of the world's most popular mainstream tourist destinations thanks, in part, to low cost airlines and the miles and miles of Costa Del Sol beaches.
Castillo de los Mendoza
Reachable with an easy 40 minutes bus ride from Madrid, Castillo de los Mendoza sits above the little town of Manzanres el Real. Admittedly it's a heavily restored castle but it you're a castle lover then this should firmly be on your list of things to see.
The capital city is not very well commodified for tourism. Once you discount the afternoon siesta, Madrid really comes alive after dark. The residents eat at midnight, roam the streets until dawn and love nothing more than a night on the tiles.
Madrid also has a long love affair with bullfighting, a tradition which still continues to this day. I personally would love to instead have the "bull fighters" fight one another to death. No need to have the bull in the ring who never wanted to be there to be tortured for entertainment. Two willing bull fighters to the death - the plus side is every match reduces the idiot population by one.
Ibiza is all about sun, beach and partying - although some people go overboard. They will get wasted on drinks and drugs, beat the crap out of each other, vomit, urinate, expose themselves and harass the locals. I skipped all the big famous discotheques because the prices were too extortionate and I avoided San Antonio after midnight because I did not want to venture into a Jurassik park.
Marbella has long been known for being a playground for the rich and pompous. Lavish retreats, villas and yachts line up the coastline, and there's a lot of flashy cars. The pool parties were super fun, especially Sisu, Nikki Beach & Ocean Beach even though they are magnets for people who parade themselves up and down with the look at me face.