The fort area itself is on an impressive scale, and is free to enter. This is also true of concerts that are held on summer evenings. Many ascend by lift from the promenade area (you can't see it - it was cut into the rock), although the walk up from the centre of the city is well worth the effort. Recent efforts have been made to create a park on the lower slopes, although it will take a while to mature. Best of all (especially when the sun is in 'scorchio' mode) is to ascend by list and then come down via the new walkway that ends up near the market area.
Some say that if you stand in the Marina area you can see the face of a moor in the rock - maybe after a few too many Sangrias, but I couldn't.

