The Pacific’s greatest cache of fossils, including those of enormous, long-extinct waterfowl, may lie in the depths of the largest limestone cave in Hawaii. Exposed by a sinkhole thousands of years ago, the cave is managed by paleoarchaeologists and conservationists David and Lida Pigott Burney, who have opened it for fascinating docent-led tours. After you make the slow, bumpy drive through former cane fields near the Grand Hyatt Kauai, a short walk takes you to the small entrance to the cave—stay hunched until you see sky overhead. Non-native tortoises, abandoned as house pets, help keep the vegetation down; visit their sanctuary outside the cave, where the Burneys are restoring native plants. Admission is free, but please donate toward upkeep and research. Tip: Rough roads may make it easier to park near the arena at CJM Stables and follow signposts north.