Makauwahi Cave is located at Mahaulepu Beach and not many people even know it's there and they are missing out! If you head to the south end (cliff side) of the beach there is a creek that flows into the river, take a right and head over the small bridge. You will see a small hole in the the wall -- you may think when you get there that you've gone the wrong way, but don't worry you're not lost. You just have to simply crawl through the small crevice that opens into the magnificent Makauwahi Cave.
This massive cave and sinkhole is considered to be on the richest fossil sites in the Pacific. The sinkhole is the main attraction at the 42-acre Makauwahi Cave Reserve. Dr. David Burney, a paleoecologist who manages the reserve, was among the first to begin excavating in the cave since 1922. Since then, this collapsed chunk of earth has showed scientists a view of the last 10,000 years of Kauai’s history.
The sinkhole’s layers of sediment have preserved records of floods, hurricanes, droughts, a massive sunami, the pollen of extinct plants, and lots and lots of bones, including those of several extinct animals like the moa-nalo, an endemic flightless duck, and a giant owl species.
The reserve offers free guided tours of the cave four days a week, during which visitors can see some of the fossils and artifacts that have been unearthed over the years — from bones and shells to early Hawaiian fish hooks and tools. Guests can also visit with the several giant tortoises that roam the area, serving as natural lawnmowers for the area’s invasive species.
So make sure when you are looking for something to do in Poipu, to put the Makauwahi Cave at the top of your list. Especially since it's a great thing for the whole family.