The boat pulled up to a creaky wooden dock that jutted out into a bay on the leeward side of Koh Surin Nua. We disembarked and hired a longtail boat to take us snorkeling. While waiting for it to arrive (Thais never hurry), we explored the island. There were a dozen small thatched huts and a little visitors center, tucked under a Banyan tree, that looked out onto an emerald bay from within a dense tropical jungle. Thai tourists, what few there were, smiled at us in a way that made me think we were in on the same secret.
Darcy was living in Thailand then, across the street from the Andaman Sea. She was teaching English but spent all her free time diving, and had heard that the Surins were, in dive slang, wicked. Which is to say that they had one of the best reefs in all of Southeast Asia.
The longtail brought us to a channel between two uninhabited isles, dropping us off before motoring on ahead to where the current would carry us. The Surins have been a national park for nearly three decades, and the overfishing and dynamiting that have destroyed most of the world’s reef systems have barely touched this one. As a result, healthy corals—and natural predators—abound.
Small, brightly colored fish (blennies and dottybacks and damselfish) were hiding. Unsettling schools of big snapper and young barracudas prowled the water—and blacktip reef sharks made shadows along the seafloor.
Darcy dove down to search for nudibranchs, and I dove after her, hooking my thumb on a brain coral to steady myself. She quickly grabbed my wrist and shook her head: Everything around us was living and easily damaged by touch. Among the hard coral we saw a moray eel, its mouth agape, with a cleaner shrimp scrubbing away at the eel’s small, sharp teeth. Then suddenly the moray hiccuped and swallowed the shrimp whole. We looked at each other wide-eyed and agreed: That was rude.
I surfaced and drifted over the reef, then took off my mask to defog it. I rested for a moment, floating in the warm salt water, and watched the longtail bobbing in the distance. We were just 35 miles off the mainland, but it felt much farther.
Vitals: Fly in to Phuket from Bangkok (six flights a day from $75; thaiair.com) and stay nearly a hundred miles north at the Golden Buddha Beach Resort (doubles from $85, three-night minimum; goldenbuddharesort.com). The speedboat to the Surin Islands picks guests up at the Buddha’s private peninsula ($10). Visit November through May—before monsoon season when the seas are rough and rains torrential. Overnight camping in Mu Ko Surin National Park starts at $20. Park admission is $6.