Cuba lies between the Atlantic to the North and the Caribbean to the South. It has traditionally been quieter than many Caribbean islands because of the difficulties of getting here from America. This may soon change.
There are many diving areas along Cuba's 5646 km of coast. The Isle of Youth (Isla de la Juventud), for example, is a marine reserve which is sheltered from the prevailing South East winds. It has caves, drop-offs and wrecks. Some of the best diving though is at the Jardines de la Reina archipelago, which you reach by liveaboard.