Today, I hiked the small mountain (512m or 1679 feet for the non-metric folk) called Tibidabo. It's not a very long or arduous walk, but it was a beautiful one. The mountain overlooks the entire city, and while the amusement park on top of the mountain may not be particularly interesting, the view is probably worth it!
On top of Tibidabo there is a small amusement park and church that date back to the turn of the 20th century. I didn't take any photos of the church/park, mostly because I figured you could find better ones online anyway. :)