Waianapanapa Falls.

This is a not to be missed stop along the Road to Hana! A 122-acre (49-hectare) state park featuring a scenic black-sand beach (with treacherous waters; swimming is not recommended), sea caves, and a rock arch. Hike shoreline trails to the sea cave, where the water occasionally turns blood red due to the presence of millions of tiny shrimp. Also here: remains of the old King’s Highway, the first road built around Maui. Hana Picnic has all the information, check them out.