Ko Hong

This guide to Ko Hong in Krabi describes the enclosed lagoon locals call Thale Nai, the inner sea, reached only by threading a longtail boat through a low sea cave. It explains how the cliffs ringing it formed roughly 250 million years ago on an ancient seabed, then were hollowed into rooms like this one by rainwater over millions of years. It also reaches down the coast to Khao Khanap Nam, where archaeologists found people sheltering in limestone caves for thousands of years. Look up at the ring of open sky the cliffs still allow above you.