There was a flea market next to the fort. It was very good.
The street markets sell budgies in cages.
There's a sex museum somewhere on La Ramblas. It's just some porno paintings and antique sex toys.
Sagra Familia was interesting. There were street entertainers opposite posing with a baby doll because they were pretending to be Mary and Joseph !
Barcelona Cathedral is a different building to this.
There's a walking tour around the city with signboards at various points.
The Picasso museum is interesting. Basically, he could paint properly IMO he just produced any old shit once he had established his brand.
As has been mentioned, is Park Guell is good and the little house now museum where Gaudi lived in the park.
The huge food market already mentioned sells, amongst other lovely things, sheep heads with their eyes still in !
If you go to the beach, you can see the Olympic stadium and the whale on top of it. There's also a structure, somewhere on the beach. No indication what it is or why it's there. It's pretty much a modern art Folly. If it's still there.
We ate paella at an open air piazza.
There was a storm at night when we were there. It lit up the alleyway in the old town where we were staying better than any horror movie !