Looking south from the top of Bastion 'C', you can see the wreckage caused by the 1916 blasting project. Engineers wanted to knock the old fort's walls down a little to open up the field of fire for Battery Pensacola (out of frame to the left, though you can see some of the earthen embankment covering the southern face of the bunker).
On the right is what's left of the southwest wall; the blasting cracked those big arches along the wall's entire length. I'm guessing that the concrete was laid down in an attempt to stabilize the damage.
Straight ahead are the gaping arches of the south cistern, where rain water was captured and stored for drinking. To its left is a pile of earth and rubble, the remains of the south wall's casemates and quarters. The arches and the facing of the cistern were destroyed in the same blasting.
Given this and the destruction of the fort's northwest corner in an 1899 explosion, vastly more damage was done to Fort Pickens by her caretakers than by any enemy.