The way to make this trip special is to catch the 8 am flight by seaplane from Key West airport and be the first on the Dry Tortugas for at least a couple hours before the catamaran ferry appears with the hordes. You get to walk the huge Fort Jefferson around the top of the unprotected parapets and then go back to sea level to walk the bird sanctuary beaches. It's a testament to technology that this fort became obsolete as the civil war armaments industry developed and adopted the rifled barrel guns which could destroy the brick walls of the fort at much greater distances than cannon balls! The fort ended up being a prison for deserters. It's a tad pricier to fly to Dry Tortuga than take the ferry but I think its well worth the extra expense especially if there is a rough sea or big swell out there which makes the long ferry ride very uncomfortable. Flew over the Spanish galleon Atocha wreck made famous by Mel Fisher and the recovery of $450 million in treasure but the water visibility was too cloudy to see much.
