West Maui
Natural tide pools on the lava shelf near Kahakuloa. Swim only in summer calm; in winter the waves wash over the pools and people have been swept off. Twenty minutes of scrambling down from the lot.
No booking, free. Park at the dirt pull-off on Honoapiʻilani Highway north of Nakalele and scramble down the lava trail; no facilities, and go only when the sea is flat.