Have you been to the largest all-masonry fort in the United States? Fort Jefferson, in the Dry Tortugas is a worthy day trip from Key West. Plan to ride the ferry, take your camera and snorkel to this National Park for a day of history, nature, and a kaleidoscope of ocean blues and greens. The variations in the colors you see when viewing the water are due to the shallows and depths and what lies below the surface. Take plenty of drinking water for this adventure.