There's much to like about this 5-acre island under the Old Seven Mile Bridge. You might even recognize it from one season finale of the TV show The Amazing Race. You can reach it via a ferry that departs from behind the visitors center (look for the old red railroad car on Knight's Key, MM 47 OS). Once there, tour the island on your own or join a guided tour to explore the buildings that formed the early-20th-century work camp for the Overseas Railroad that linked the mainland to Key West in 1912. Later the island became a fish camp, a state park, and then government-administration headquarters. Exhibits in a small museum recall the history of the Keys, the railroad, and railroad baron Henry M. Flagler. The ferry ride with tour lasts two hours; visitors can self-tour and catch the ferry back in a half hour.