A tropical permafrost lake
Lake Waiau sits at about 13,000 feet of elevation near the summit of Mauna Kea on the island of Hawaii. It’s the only permafrost lake in the tropics, and though it shrank to about 2 percent of its previous size several years, it has made a comeback and can be reached by hike off the road to Mauna Kea’s summit. On the same island, you can also visit a Papakolea Beach, which features green sand thanks to a large supply of the mineral olivine.