Koh Tarutao was once Thailand's version of Devil's Island, the infamous French prison off the coast of South America. Like Devil's Island, Koh Tarutao was surrounded by the sea and completely cut off from the public. Thankfully, times have changed, and Tarutao is now a pristine national park. The prison guards and inmates are gone, but the bizarre story of how they banded together to become pirates during World War II remains.

The Mu Koh Tarutao-Koh Adang archipelago, off the southernmost Andaman coast of Thailand, is a national park comprising 52 islands, lushly forested and dotted with beaches. The main island, Tarutao, from which the archipelago takes its name, is accessible by speedboat from Pak Bara harbor. On the island itself, you won't find 7-Elevens, ATMs, luxury spas, go-go bars, tailors, or jet skis.

Instead, Tarutao offers endless stretches of quartz sand, a bottle-green sea, simple bungalows, jungle roads, and at the end of the day, a cold beer and pad thai at a beachside canteen. What more could you want?

The uninhabited archipelago lies as far south as possible in Thai waters. (The Malaysian island of Langkawi is only five kilometers away.) The islands' towering rock formations and crystal-clear waters are part of the country's first National Marine Park and, with the exception of the small island of Koh Lipe, remain largely undiscovered by large tour groups and mass tourism.

Those who have made it here from the hustle and bustle of Bangkok or the crowds of Phuket are rewarded with the pure simplicity of this place. As a bonus, there are sea eagles, macaques, monitor lizards, and pristine, untouched beaches. Experience the real Thailand.

Koh Tarutao, the largest island (152 km²), offers bungalow complexes near the National Park administration building at the Phante Malacca arrival pier, as well as on Ao Molae and Ao Son beaches. The accommodations are basic and therefore inexpensive, starting at around US$25 per night. My bungalow, right on Ao Molae beach, had a somewhat run-down but adequate bathroom, a clean bed with a mosquito net, and—noisily squawking in the rafters—probably the loudest gecko in the world. A generator provides five hours of electricity per night. Advance booking is required; alternatively, you can rent a tent from the park office and camp under the stars.

It wasn't always so peaceful. Between 1938 and 1949, Tarutao was the Andaman equivalent of the infamous "Devil's Island" penal colony in French Guiana, made famous by the novel and film "Papillon." Up to 3,000 Thai convicts were imprisoned on Tarutao at any one time, separated from the mainland by a 30-kilometer-long underwater trench teeming with sharks and crocodiles.

During the Japanese occupation of Thailand in World War II, food supplies from the mainland were severely rationed, and a famine broke out on the island. In desperation, some convicts and guards turned to piracy in the nearby Strait of Malacca. Their attacks on passing Malay and Penang merchant ships became increasingly brazen, brutal, and lucrative. They were so successful in their plundering that they continued their violent activities even after the war ended. The pirates were finally defeated in 1946 by a 300-man British Royal Navy commando unit attacking from Malaya.

The prison closed in 1948. Today, you can cycle or walk to Ao Thalo Bay, where the main prison was located. The jungle and looters have long since reclaimed the original buildings, but well-maintained paths lead to several reconstructed structures, and illustrated signs depict daily life and death in this tropical purgatory.

Those who have enjoyed the unspoiled island of Tarutao and its memorable early evenings will be either delighted or repelled by the contrast to nearby Koh Lipe (pronounced Lee-pae). Lipe, Thailand's southernmost island, was not included in the national park because it was already inhabited by the Chao Lay sea nomads, who over time leased much of their land for tourism. An hour's boat ride south of Tarutao brings you to Lipe's bustling Pattaya Beach, where you are immediately swept up in the consumer frenzy of Walking Street.

Pizza, supermarkets, dive schools, and cool bars await you. The streets are lined with restaurants, stalls, and lodges. Not a macaque or monitor lizard in sight. Instead, you'll find small motorbike taxis, breathtaking sunsets, easily accessible reefs, snorkeling and diving excursions, and warm water in the shower. Birdwatching on Lipe focuses more on eagles than sea eagles, but it's still a blast. The lagoon shimmers in Tahitian turquoise – something you never saw on Devils Island.

Getting there: Fly or take a bus from Bangkok to Trang; then transfer to Pak Bara and from there a two-hour speedboat ride to Tarutao. Accommodation: See Thai National Parks (www.dnp.go.th). Season: November to April. (The national park islands are closed during the monsoon season. Koh Lipe remains open.) www.kotarutaothailand.com; www.kohlipe.net