Once you land at the Dry Tortuga’s you cross the tiny strip of sand where the plane is moored and approach the entrance to Fort Jefferson. The fort covers over 90% of the island and is constructed of 18 million bricks. There is a small adjacent isle that is connected at low tide. There is a third one that extends a bit further toward the mainland that is a roosting place for Magnificent Frigatebirds. This is the most northerly locale for these amazing birds.