A perfectly circular beach at the bottom of an open crater in an island, invisible from outside, reached only by swimming…A perfectly circular beach at the bottom of an open crater in an island, invisible from outside, reached only by swimming through a 20m tunnel with barely a metre of air above you. You surface inside a roofless cave with a sand beach and a circle of sky. Blue-footed boobies nest on the cliffs above. The crater was reportedly created by Mexican military bomb testing in the early 1900s, which makes the most beautiful hidden beach in the Pacific an accident of ordnance. Cousteau campaigned for its protection in the 1960s; it became a national park in 2005 and visitor numbers were capped in 2016 after coral damage from 2,500 daily visitors. Anchorage: Anchor off the islands in the designated zone; landing restricted. Hazards: The entry tunnel has less than a metre of headroom at high tide and surges. Time it on low water with a guide. Altro