Lastly we took a cable car up to the old fort that has been guarding Barcelona for centuries. It's got great views over the entire city and the sea, so it's worth the trip. But the castle itself is pretty low key. Much of it is underground, so it's not particularly photogenic. There's also a huge cable car ride all the way down into the city from the fort, but it was mobbed, so we walked down instead, and walked all the way back toward the hotel for one last beach walk.