Turn left at Phuket: Thai haven the 'tourism monster' hasn't discovered yet

Forget Phuket. You've landed at its airport, now hang a hard left. Aim north, traveller, not south. And don't stop until you've crossed the bridge to mainland Thailand.

I do just that. Within 20 minutes I'm in green, jungled Phang Nga province. Real Thailand. Palms and sea pines instead of jet-skis and high-rise. Empty beaches. My mission: to follow Highway Four up Thailand's west coast, via Khao Lak to old Ranong. Three-hundred kilometres of under-tourism.

The Andaman Sea flickers behind a curtain of tall son talay sea pines. Natai, the first mainland beach, stretches into the distance. Seafront eateries, small resorts, a turtle sanctuary and not a speedboat in sight. But I'm aiming further, to Khao Lak, a loosely defined area that stretches up the coast well beyond its original namesake beach.

"It looks like Phuket did 40 years ago," says a veteran Danish visitor, reminding me that it was early Scandinavian travellers who helped put Khao Lak on the holiday map. She adds, chuckling, "Back then, first I had to ask how to pronounce Phuket politely."

This isn't Khao Lak's first tourism rodeo but it still looks like an Andaman coast, not a wannabe Cancun. Its resorts are tucked behind the frontal dunes and screened by casuarinas while the busy highway with its restaurants, markets and dive shops sits well inland.

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I'm travelling solo in monsoon season, heading slowly north, exploring. My base will be the laid-back Avani+ Khao Lak Resort on long, sweeping Bang Sak Beach. My poolside suite comes with midnight fireflies and a monsoon moon racing the clouds. But first things first: at the in-house Beach House restaurant I top-off a day of good travels with my favourite tropical treat, grilled lobster, a chilled Singha and mango sticky-rice dessert.

Next morning I step around a slo-mo roadblock, two turtles dawdling on the beach path. A wake-up bodysurf, a breakfast buffet raid and then it's time to start exploring. First stop is Bang Niang, mid-point on the Khao Lak holiday shore stretch. The village market is a cornucopia of everything you might ever (or never) want to wear now, haul home or query later. Tons of cheap, colourful clobber, plus bargaining fun. Or just more fast fashion? I'm a shopping fail - as in: "Do I really need more stuff to lug around?" Negative. I divert to a hawker stall for a charge of Thai gafe boran - "ancient coffee" - and keep moving.

Languid Khao Lak is the springboard to Thailand's Andaman Sea islands, including the Koh Similan and Koh Surin archipelagos. I've snorkelled before among their fragile, luminous corals but these marine national parks are closed during monsoon. Otherwise, the April to October off-season months are an excellent time for travelling this coast. Buckets of rain, buckets of sunshine, no crowds.

Queensland has its Gold Coast but Thailand uniquely boasted a Tin Coast. Until the 1960s, the Andaman seaboard boomed with a Golden Age of Tin. And then the lodes ran out. Where they once had dug tin, Phuket entrepreneurs transformed the old pits into resort lagoons and by the 1980s were mining tourist gold. The island now sees 10 million arrivals a year. While other mining towns missed the visitor invasion, their 19th-century architecture survived, near-forgotten and almost intact.

I head north to Takua Pa. The streets of its Old Town are lined with Sino-Portuguese shophouses, the sort that Singapore once demolished (only to later rebuild as replicas) and that Phuket has tricked-up as boutique hotels and hip restaurants. Hokkien Chinese culture dominates here, reflecting the immigrant settlers who worked the ore. In the mix were Cornish engineers and even an Australian who invented the world's first tin mining dredge.

With curious tourists and Thai "sea-changers" rediscovering Takua Pa, its colonnaded shophouses have scored an overdue lick of paint. There's a Sunday street market. New murals dance along the walls beside traditional tea shops and its open-fronted barbershop thrives. The old pagoda-style temples endure. An iron bridge across the river is a nostalgic throwback to the days of "waste not-want not". Back in 1968 the locals built it from the metal of an abandoned dredge.

"Please close the window of your treehouse before you go out," cautions the manager of Khao Sok Nature Resort. I've moved on, reluctantly, from the Avani's seductive spa and sunset bars to Khao Sok National Park, a differently seductive, 740-square-kilometre rainforest wilderness. My treehouse resort sits outside the park border, a line that the forest's langur monkeys happily ignore. The pickings from a tourist's unguarded room - chocolates, binoculars, passport - can be fascinating, if not devastating.

Windows secured, I head to Cheow Lan Lake, the jewel at the heart of Khao Sok. I hire a kayak and paddle out. Karst limestone walls soar above the waters while the dense rainforest is home to civet, eagles, pangolin and other species. You can hear but rarely glimpse a booming gibbon or barking deer, but the langurs are unmissable as they trapeze from tree to vine like miniature mad Tarzans in a "Look, Ma! No net!" circus riot.

Khao Sok is worth many days of hiking and kayaking. I have just two, and so I move to the Elephant Hills Lake Camp, a raft-house resort that's moored by the lake shoreline. Joining other kayakers, I paddle along the park's languid Klong Sok River. The silence is broken only by birds (there are 180 species here) and our muted exclamations at spotting an electric-blue kingfisher or a tree viper looped on a branch above our heads.

Buses are scarce on this coast but there's one to Ranong, 170 kilometres north. So, it's goodbye to the coast's creamy coves and firestorm dusks. Flatlands of coconut plantations and oil palms give way to riotous jungle as Highway Four winds through the Tenasserim Hills, the ancient tailbone of the Himalaya's spine, which extends, incredibly, from Tibet to Phuket.

The bus is quiet but for the maraca rattle of its old bones. No roaring rom-com video or pop. Shrouded Muslim women come and go. Villages, mosques, a forest monastery, a military checkpoint. We're at the narrowest pinch of the Malay Peninsula, where just 60 kilometres separates the Indian Ocean from the Gulf of Thailand. I nap for a while, waking to see a cliff that weeps two slender, long-drop waterfalls. Namtok Ngao, the liquid gateway to rainy Ranong.

The tourism monster that ate your last, favourite "undiscovered" town somehow missed Ranong. At the northern tip of Thailand's Andaman coast, it is another former tin town. Lacking upsized resorts, a cash-cow beachfront and honking tuk-tuks, it instead offers dawn monks, real markets and Ruengrat Road's line of classic shophouses. The latter are being tweaked, their louvred shutters and loggia archways now back in vogue.

Ranong is the capital of the rainiest province in Thailand and principally a fishing and trading port. For island-hopping visitors it is mainly a launching ramp to Koh Phayam and little Ko Chang, or Myanmar's Mergui Archipelago. Think hornbills, sea gypsies, no-car islands. As well as offshore adventures, Ranong for me is a place to simply ramble, eat, read, investigate. But there's one "must do" I never miss, the public hot springs.

"Please hold out your arm," says the front desk attendant. "You need blood-pressure test." What? This is a new one. After a week of lizard-level Andaman ease, how can I seem stressed to the point of needing a medic?

"New rule," he explains. "Everyone must have check before enter." Blood-pressure rising, I submit my arm, get cuffed, get tested and pass. Blood-pressure subsiding, I enter the pool complex built along the bank of a rushing river.

There's a series of steaming, sulphur-free pools of different temperatures. Unwisely I drop into a 40-degree pool but within minutes I flee, scalded lobster-like, to a moderate, 30-degree bath. Immersed there, I simmer, content, chilling hot in cool Ranong.

Thailand's northern Andaman coast is littered with islands. From the south ...

Koh Similan and Koh Surin groups: Two marine parks 50 kilometres offshore, with brilliant corals and snorkelling. Crowded at times. Reach the Similans by speedboat from Taplamu, and the Surins from Kurabhuri. Limited camping; book early. thainationalparks.com

Koh Phra Thong: Large and unspoiled. Empty beaches fringed by palms, some lodge accommodation. Stay longer. kohphrathong.com

Richelieu Rock: Legendary seamount, home to whale sharks and hammerheads. Access via liveaboard dive boat. diverichelieurock.com

Koh Kam and Koh Kang Khao: Pristine isles well south of Ranong. Hard to reach but stunning. thailandtourismdirectory.go.th

"The elders told us that if the water recedes it will reappear in the same quantity," said Sarmao Kathalay, a Koh Similan Moken "sea gypsy". As the ocean receded on Boxing Day 2004, the Moken knew that "the wave that eats people" was coming. They escaped to the hills. On the mainland buildings were reduced to rubble and thousands of lives lost.

Little evidence now remains of that once-in-a-millennium day. A police patrol boat sits two kilometres inland, dumped there by the ocean 20 years ago. A euphemistically worded sign, "Permanent Residence of the Tsunami Victims" points to a cemetery. Two 70-tonne fishing trawlers remain beached in front of in Ban Nam Khem's commemorative museum. The nearby Tsunami Memorial Wall rears like a wave of memory, its name plaques recalling victims, foreign and Thai.

Despite whispers that the supposedly "ghost-fearing" Thais would never return to Khao Lak, they did so in numbers; as have foreigners. Today, the coast is healed but nothing is forgotten.

Transport: There's little regular public transport. Book an airport transfer to your accommodation, or load the Grab rideshare app. Taxis: always negotiate the fare first. Long-distance buses: 12go.com

Season: Khao Lak is a year-round destination. The weather is wet and hot during monsoon months, generally May-October; dry and cool(er), December-March.

Caution: Ocean drownings are too common, especially in monsoon. There are no lifeguards.

Don't miss: A daytrip (or longer) to the Similan or Surin islands, or other less busy ones. At Ban Namkhem see the Tsunami Museum and Memorial Wall. At Ranong simmer in the hot springs.

Accommodation: As well as the family-friendly Avani+ Khao Lak Resort (avanihotels.com), there is a wide range, from bungalows to luxury resorts, including Khao Sok Nature Resort (khaosoknatureresort.com), Elephant Hills Rainforest Camp, Khao Sok (rainforestcamp.com); Sino Mansion, Ranong (via a booking site); and Numsai Khaosuay Resort, Ranong (numsaikhaosuay.com).

The writer travelled at his own expense with accommodation support from Avani+ Khao Lak Resort.