Descend into a whimsical world where what looks like rocks are really living creatures, where schools of fish come dressed in rainbow-colored uniforms and where beautiful flowers play hide and seek with other sea life.

If you think the U.S. Virgin Islands offers only sun, sand and sea, you're missing half the fun - the undersea world is as easy to access as the islands themselves and equally as exciting.

The many reefs which rim the U.S. Virgin Islands of St. Thomas, St. Croix and St. John offer countless hours of underwater exploration for both beginning and experienced divers. Rock-like coral heads ar e actually mini-ecosystems housing a rich mix of fish. Several shops sell water-proof booklets that aid in identifying undersea flora and fauna. Divers have an advantage over snorkelers in being able to descend deeper and see spectacular sunken gardens at the bottoms of dramatic drop-offs. Visibility is excellent, up to 120' in many locales. Even night dives are spectacular when nocturnal sea creatures voraciously lap up microscopic morsels with their tendril-like tongues.

Diving in the U.S. Virgin Islands is easy, enjoyable and offers something for everyone. There's no need to be an excellent swimmer, just comfortable around the water and in general good health. Beginner s will find conditions excellent - warm and calm seas, great visibility and much to see starting at just 20' to 30' - for short resort or full certification courses. For experienced divers, there are some 58 dive sites accessible by beach or boat, to reefs or wrecks, during daytime or at night.

To get air tanks, rent equipment, obtain air fills and join others on guided tours, divers must show their C-card - certification of training card - from a recognized international program.

Most U.S. Virgin Island dive operators offer full certification courses. These are intensive 32- to 40-hour open-water trainings can be accomplished in as little as 3 very full days. However, dive operators usually recommend that dive students do their book and basic pool work at home, then transfer from their home instructor to Virgin Islands to finish up their four open-water dives and complete qualifications for C-card. Minimum age for PADI instruction is 12 and certification must be upgraded at age 15.

Two- to three-hour "resort" courses are available for sampling the sport of diving. These short classes, which do not count towards certification, start out in shallow water in a pool or off a beach, then progress to a short 30 to 40 foot dive.

Buying dive packages offers the advantage of be assured a seat on a dive boat, especially important in-season from December through April. Packages vary in price, depending on if instruction is included or other amenities like a combo- hotel, villa, condo or guest house rental is part of the deal too. However generally, packages do help to reduce the cost of individual dives.