Rarotonga is one of those islands that old South Seas hands recalled fondly when the talk around the bar turned to the quintessential island paradise. Long a favorite with sailors, Rarotonga, with its volcanic landscape of jagged peaks and deep valleys, is the only mountainous island in the Cook Islands. Its interior is mostly lush rain forest, and miles of white-sand beaches and an uncommonly clear lagoon fringe its shore. Dive shops on the island lead trips to about 40 sites that cover the full gamut of the water world: steep drop-offs, wreck dives, canyons, swim-through, coral-laden reefs and, for adrenalin junkies, shark dives. Visibility averages about 100 feet, and thanks to a five-year-old marine conservation program, the fish life in the once-over fished lagoon in making a strong comeback. Offshore, fishermen can count on catching yellow fin tuna, mahi-mahi, wahoo, and spotting humpback whales during their July-to-October migration. Big-wave surfers keep their eyes on the horizon at Avatiu harbor in Avarua.