The Abacos - Top of the Bahamas Named after Great Abaco, the largest landmass in the chain, the Abacos span nearly 130 miles in length and include Walker's Cay in the north and Hole in the Wall at the southernmost tip. In between lies a chain of islands and cays protected from the open Atlantic by fringing barrier reefs. The outer reefs, islands and cays create a large, naturally protected expanse of water that is commonly referred to as the Sea of Abaco, which has made the Abacos a favorite cruising ground for yachtsmen. For divers, this topography sets the stage for an assortment of beautiful, quaint little cays and colorful shallow reefs in the 10- to 60-foot range. A must-see site is Coral Caverns off Green Turtle Cay: It features a series of dramatically tall coral formations that create a catacomb of twisting alleyways and expansive swim-throughs. Farther south, Great Guana Cay offers miles of spectacular dune-lined beaches with nearshore reefs - the most spectacular of which are located along its northernmost shore. Throughout the Abacos is a series of national preserves and parks, including Fowl Cay National Preserve and Pelican Cays National Land and Sea Park. The larger of the two Pelican Cays' parks protects an extensive area of shallow reefs and mangroves harboring an array of marine life. Because fishing is strictly controlled, the reefs are abundant with sea turtles and groupers. If historic shipwrecks are your passion, visit the USS Adirondack. This Civil War gunboat struck a reef off the north end of Man-O-War Cay in 1862, the same year that it was built. While shipworms have eaten nearly all of its wooden timbers, divers will find among the wreck's debris field two 13-foot cannons and boilers from the Adirondack's steam engine. Great Abaco might be the largest and most talked about of the chain, but it's the maze of cays and islands that thread through the Caribbean Sea that make the Abacos Islands the dive paradise that they are. QUICK GUIDE Dive Abaco (diveabaco.com), located in Marsh Harbour, Great Abaco Island, specializes in referral certifications, Open Water certifications, specialty instruction and dive tours aboard its 10-passenger, 28-foot Delta and 16-passenger, 30-foot Island Hopper. Dive Abaco runs many charters out to the Fowl Cay National Preserve and neighboring Pelican Cays National Land and Sea Park. Shark dives, island-hopping adventures and sunset cruises are also available. For more information on diving in the Bahamas, contact the Bahamas Diving Association (bahamasdiving.com).