Fort Pickens near Pensacola Beach, Florida, exhibits several contrasting building styles, two of which can be seen in this shot taken in the undercroft of the fort. The original brickwork comprises aesthetically pleasing domes and arches while later additions (I presume) tend towards a more angular, functional style. Even later additions, not visible here, are in concrete with the typically brutalist style seen in 20th century gun emplacements.
For the technically inclined...