Trunk Bay, St John, U.S. Virgin Islands
As you can see, the water was breathtakingly beautiful. Snorkeling here felt like floating in a giant, warm, sandy pool. The guide book I had warned us that this beach would be crowded, but that wasn't a problem when we were there (February). There is also an underwater snorkel trail with underwater signs explaining where to go and what you're seeing. There were shower facilities, a snack hut, and a snorkel renting station at the trail on the way to the beach. We brought luna bars and peanut butter sandwiches with us.