Scuba divers and snorkellers will find endless opportunities along the reefs surrounding the islands of St Thomas, St Croix and St John. The US Virgin Islands are among the most beautiful diving areas in the world with coral reefs, crystal clear water, dramatic drop-offs, underwater caves, shipwrecks, and a variety of marine life, including the region's famous sea horses. Along the north shore of St Croix is a fantastic underwater wall that offers caves, pinnacles and tunnels and opportunities to mix with deep-sea sharks and eagle rays. Other sites of note are the 1,000ft (305m) drop-off of Salt River Canyon, Frederiksted pier and the wall at Cane Bay. Between St Thomas and St John the waters of Pillsbury Sound contain several shipwrecks, and the best dive site off St Thomas is Cow and Calf Rocks. Snorkellers should head to the unrivalled Buck Island Reef National Monument off St Croix for beautiful coral reefs, Magens Bay or the marine sanctuary on St Thomas, or the coastline of the Virgin Islands National Park on St John.