Hawaii's famous green-sand beach is located at the base of Puu o Mahana, an old cinder cone spilling into the sea. The place has its problems: It's difficult to reach; the open bay is often rough; there are no facilities, fresh water, or shade from the relentless sun; and howling winds scour the point. Nevertheless, each year the unusual green sands attract thousands of oglers, who follow a well-worn four-wheel-drive-only road for 2 1/2 miles to the top of a cliff, which you have to climb down to reach the beach. The sand is crushed olivine, a green semiprecious mineral found in eruptive rocks and meteorites. If the surf's up, check out the beach from the cliff's edge; if the water's calm, it's generally safe to swim.