St. Thomas and St. John are two of the United States Virgin Islands (USVI) and there is just a short ferry ride separating the two. Charlotte Amalie, the capital of the USVI and its biggest city, is located on St. Thomas.
The most popular beach on St Thomas is Magens Bay. The beach has great sand, clear and warm water, and it is considered by many to be one of the most beautiful beaches in the world, although in my opinion Trunk Bay of St. John is even better.
There is a lot of good snorkeling and scuba diving all around the island. Many of the resorts on the beach are within easy walking distance from a beach with good conditions.
St. John
St John has a little over 4000 residents on the whole island. There is no airport on the island, so the only access is by boat. There is an hourly ferry from St Thomas and also a daily ferry from Tortola (in the British Virgin Islands). The highlight of most visits to St. John is going to Trunk Bay. This is one of the most picturesque beaches in the world and has a small island off the beach. There is an underwater snorkel park just off the beach with signs explaining some of the features to look for.