That that looks like Fort Jefferson/Dry Tortugas Nat. Park. If so INCREDIBLE place.
Every ounce of water, all sand and mortar shipped there to build this part of the US coastal
defense system way back in the day. The masons who built this place were artisans! Most
famous for housing Dr. Samual Mudd.
We were stucked there for several days/tropical storm, but what a place to get stuck!