We had anchored off the southwest end of Koh Muk, a tiny island in the Andaman Sea off the west coast of Thailand. As we leaped in the water off the stern of Orion, the 60-foot sloop we were sailing on down the Malay coast, we faced a sheer coral tower that rose like a skyscraper a thousand feet out of an emerald sea. With flippers on our feet we headed toward a frown in the cliff at the waterline.

A sea swell like a monster’s breath drew us in and blew us out of the opening, which we entered with trepidation and on the assurance of Skip Jones, sailasia@yahoo.com, the captain and owner of the Orion, that the far end of this mysterious and forbidding tunnel will reveal astonishing natural beauty.

As we swam our voices echoed off the black coral rock. We followed the thin beam of Skip’s underwater diver’s flashlight. With a last look back distant ambient light turned the sea in the tunnel an emerald green such as I would not have expected ever to see with my own eyes. Then total darkness surrounded us.

I grasped Fraser’s hand, and Charlie took Molly’s.

“It’s been awhile since I was here,” Skip said, though we couldn’t see him. “I don’t know for sure if this is the right way.”

We turned a corner out of even the dim light of the tunnel’s entrance. The water licked the coral walls, and with each surge, swells nudged us against the corals. We swam in the dark, the flashlight beam our only guide, with no idea where we were or how far the tunnel extended – if this was indeed a tunnel and not a sea cave. The water in this high tide under our treading feet was too deep to contemplate.

Skip’s flashlight blinked and went out. Total darkness. “It’s broken on me, I guess,” he said. “Gee, this has never happened before.” After shrieks from everyone the beam went back on, with Skip grinning from ear to ear.

Skip’s humor at that moment missed me by the widest mark I can remember, ever, which was an accurate measure of my profound discomfort at being where I was at that moment with my family. My assessment of him plummeted, though over days he would redeem himself, oddly enough, in a bat-filled cave. Good swimmers and comfortable in water, we were still babes in this Andaman Sea, far from anyplace familiar to us, in the dark of a narrow tunnel with no end, or light, in sight.

Mercifully, a glimmer of natural light appeared that we swam for. The tunnel indeed cut through the island’s coral wall. We swam out into the open sunlight. Truly, the most beautiful beach I will ever see was made even lovelier still by my bottomless relief at leaving the tunnel behind us. We had swum into what is best described as a huge elevator shaft of thousand-foot walls with tropical shrubs and trees rising up to the sky. We were encircled in this so-called “hong” by loveliness unlike any that we could have ever expected to see. A pristine white-sand beach lay 30 yards across the hong like a welcoming grin.

We were visiting this Ko Muk Hong on the second of a seven-day sail aboard the sloop Orion (a name which seas, time, winds and indifference had erased off the boat’s transom–from Orion, to Orio, then Rio and now, Io). The Io’s captain, Skip Jones, a 50-year-old who resembles an American version of the Englishman Richard Branson, with his same goatee, long brown hair, toothy boyish smile and a gold ring in one pierced earlobe, had come recommended to us by a Sri Lankan friend as reliable and personable. This was to be for us a sea voyage of destination–toward Kuala Lumpur, Malacca and the Indonesian island of Sumatra.

Right from the start, we chipped in with the chores. This was not a “charter” cruise, Chip explained to us, as much as a “cost-sharing” voyage (he needed to enter Malaysian waters to renew his Thai visa). In the spirit of All-For-One, Fraser threw a neon fishing lure over the stern while we sailed and soon had hooked a silver-skinned Bigeye trevally, which Skip gutted and filleted on Io’s teak deck and his dark-haired “mate” Samantha Tillman (a pretty New Yorker who could cook in the most turbulent tides) sauteed in butter. For her part, Molly was keeping abreast of the author George MacDonald Fraser’s “Flashman” series with such concentration she glanced up from the book’s pages only at her parents’ insistence to admire the rain forests on the islands we sailed past, the reefs and the fish schooling in the crystalline water feet below where she was perched on deck.

The night snorkeling in the phosphorescent, clear waters, scuba diving the underwater walls, the coral gardens and the tropical sea life transported Charlie to Nirvana. One night anchored off Koh Lipi, about 60 miles from the Thai coast, an excitable gaggle of crypto-hippie “travelers” invited us to celebrate a birthday on the clean white beach. We sat down with glasses of a papaya fruit punch laced with Thai vodka, and as Margaret Meade with a dying native tribe, we observed these amazing folks dancing half-naked in the moonlight. For our (and their) entertainment they threw flaming batons, juggled Indian clubs, blew into Australian aborigine didgeridoos and talked and laughed in at least eight different languages. “They look like monkeys,” observed Molly under her breath, agog at these different lives. We couldn’t help but admire their winning and earnest simplicity.

For all its uniqueness–and for all its perceived romance–this cruising life wears thin fast and, in the end, it isn’t for me. Sailing in the open sea is tedium itself. And the open sea in the close proximity of strangers is no better. I had nowhere to escape. As for familiarity, the Io soon looked like a floating Chinese laundry with underpants, ladies’ delicates, towels and pants flapping from the lines. Everything was everywhere; one night I simply bulldozed with both arms a bewildering variety of stuff from our duffels to the end of the bed. Skip said one night, observing the cluttered decks, “Yachting is an expensive way to travel Third Class.”

Fraser’s big tenth birthday came on the Andaman Sea, and by his beaming admission he never had a better one. Skip took him bogey boarding behind the dinghy and Fraser stuffed himself with blueberry waffles while he basked in the freedom of a day without paternal discipline. We had wrapped his presents in a Chinese “Special K” cereal box, a Kerala sarong, blue gingham bandana and an outdated London Daily Mail. And Charlie baked a scratch pound cake made of Hershey’s chocolate syrup and whatnot, decorated with green marzipan.

Our last night onboard Io, anchored off Langkawi Island in Malaysia, Skip mentioned a limestone cave that looked glorious in the moonlight. We glanced up. A half moon was rising. We agreed to go exploring with him only if he stopped the jokes at the expense of our fears. A short time later, girded with Tevas, bug repellent, flashlights and long-sleeved shirts, we slipped into a stream in a mangrove swamp. The cave’s mouth overhung with lianas and broad-leafed hothouse plants. The brackish water became waist deep. Our lights shone off silicates like diamonds. We went in further, heading to a limestone “cathedral” with a domed roof on which tiny, irritable bats clung in the day.

“I could make a joke here about not knowing the way back,” said Skip to Charlie. “But I won’t.”

“I want to go back,” said Molly, who later would proclaim this to have been one of the most amazing experiences of the trip. She raised her voice to the level of a whine. “This isn’t fun.”

Ploughing ahead into the tunnel over a hydrant-size stalagmite, Skip said over his shoulder, “Fun? This isn’t supposed to be fun. Fun is eating popcorn at the movies. This is adventure.”

Molly pondered these distinctions. Flipping on her miner’s head-strapped flashlight, she waded ahead with grim determination.