You may well think this enormous sinkhole is a lost world. The only way in is by squeezing through a tiny opening in a rock wall. Suddenly you find yourself in a beautiful, open-air atrium, with palm trees dwarfed by high cliffs and an enormous cave system beneath.

While this is arguably the richest fossil site in the Hawaiian Islands, very few people seem to know about it. Since 1996 it has been excavated by scientists with the help of students, volunteers and visitors, yielding fascinating results. The site has provided evidence for the widespread extinction of species in Hawaii following human settlement. Paleontologist David Burney’s well-written book Back to the Future in the Caves of Kaua’i tells this cautionary tale.

Makauwahi Cave is located at the western end of Mahaʻulepu Beach, but is best approached from above by car, then on foot. Trail guides are usually available in a self-serve box, or downloadable online. The sinkhole is currently open to visitors for free guided tours (no reservations). Check the website for up-to-date tour times and directions.