Virgin Islands
Credit: Donald Nausbaum / Getty Images

After the U.S. bought St. John, St. Thomas, and St. Croix from Denmark during World War I, Laurence S. Rockefeller donated more than 5,000 acres of St. John to the National Park Service to preserve the land. In 1962, the Virgin Islands National Park acquired an additional 5,650 underwater acres around the coastline, and today, stretches about 19 miles through half of St. John. The area is marked by white beaches, coral reefs, swampland and more than 800 subtropical plant species. 

Don't Miss:  Trunk Bay, one of the world's most beautiful beaches and hosts a 225-yard-long underwater snorkeling trail. Cinnamon Bay has an aqua sports center that can help arrange windsurfing, sailing, snorkeling and scuba diving lessons. It also has a campground with tent sites and cottages across from the beach.