The Rock Islands are roughly 445 limestone islets that rise from a turquoise Palauan lagoon like green mushrooms, each perched on a stem the sea has slowly eaten away at the waterline. Known to Palauans as Chelbacheb, they began as a coral reef that grew underwater, was lifted up by ancient earth movements, then was carved by rain and tide into forest-capped domes with deeply undercut bases. In 2012 the Rock Islands Southern Lagoon became Palau's first UNESCO World Heritage Site, and one of the rare places listed for nature and culture at once: its reefs hold more than 385 coral species, its interior hides the highest concentration of marine lakes found anywhere on Earth, and its caves and shores carry villages, burials and rock art left by people who lived here for some three thousand years before the islands were abandoned.
Most of the lagoon can only be reached by boat, threading between islets packed so close the channels feel like green corridors. Slip into the water and the reef opens a few metres down, patrolled by sharks, turtles and eagle rays; at German Channel, giant manta rays glide in to hover over cleaning stations as small fish pick them clean. The strangest swim lies inland, in Jellyfish Lake, where millions of golden jellyfish drift back and forth across a landlocked pool as they follow the sun — a population that vanished in the 2016 drought and has since returned. Between snorkels you can beach on white sandbars that surface only at low tide, or float in coves so clear the coral looks within arm's reach. The whole area is now protected: you visit on a permit through licensed local operators, and Jellyfish Lake keeps its own rule of snorkellers only.