I followed Thailand's Royal Coast and found a regal world even locals don't see

Facing a fabulous ocean isn't enough these days for an ambitious coastline. A glittery tag, like Gold, Sapphire, Emerald or d'Azure, is a branding imperative. Thailand came up with a real winner for its Gulf shoreline - the Royal Coast. And then forgot to tell the world. I'm not a monarchist (more like an escapist) but, curious about this unsung regal riviera - a 300-kilometre stretch through the western Gulf provinces of Phetchaburi, Prachuap Khiri Khan and Chumphon - I go in search.

My first royal pile is Phra Nakon Khiri ("Holy City Hill"), a summer palace built by King Mongkut (Rama IV) at Petchaburi, 120 kilometres south-west of Bangkok. The 1860 hilltop complex is an architectural tom yam, featuring a red Chinese pagoda, Buddhist chedi spire and white Italianate villa, all reflecting a modernising Siam, as Thailand was then known. Having a getaway from Bangkok worked so well that the next king, Rama V, built his own palace nearby, the elegant, Art Deco-style Ban Puen, which is now a museum. The next Rama, No. VI, created a "modest" seafront structure in 1924 - Mrigadayavan Palace - that claims the undisputed title, "longest golden teak palace in the world". Its long, raised walkways lead to spectacular sea-view pavilions, including the translator king's own writing room. In the past I've wandered unguided through the sprawling estate but visitors today usually join a tour.

The region's benign climate attracted serial rulers to build summer retreats here. Rama VII's Wang Klai Kangwon ("Far From Worries") palace, constructed in 1926, sits almost in midtown Hua Hin but is off-limits to the public. (When a rare royal is in residence, there's a Thai Navy boat parked offshore.) Instead, visit the Seven Kings Monument where the giant bronze statues of former kings rule over Rajabhakti Park.

Royals and aristocrats originally rode the train from Bangkok down to Hua Hin. This southern line launched in 1921 and its ornamental Royal Waiting Room, the most photographed building in the province, still stands on the platform. Following the railway, the beautiful Italian-designed Railway Hotel (now Centara Grand Resort) opened on the beachfront in 1923. I hit its historic Old Wing for afternoon tea and then wander through the garden's century-old topiary where the giant rabbits, birds and a massive elephant seem on the verge of springing to life.

Siam's first 18-hole course, Royal Hua Hin Golf Course, opened in 1924. Players stepped from the Bangkok train, had their caddies check the course for tigers and then teed-off. A legendary round occurred in 1932 when King Rama VII was told, mid-game, that bureaucrats and military leaders demanded that the country's 700-year-old absolute monarchy be replaced with a constitutional one. He is said to have replied to his friends, "I told you so," and played on.

Khao Sam Roi Yot ("Mountain of Three Hundred Peaks") National Park, 23 kilometres south of Hua Hin, is a maze of lakes, limestone spires and mangroves. I take the jungle path to its most visited spot, Phraya Nakhon Cave, where King Rama V meditated in 1890. You can see where he signed the wall, as did Rama VII in 1926. The cave's delicate, sun-lit central pavilion is said to be the smallest temple in Thailand.

Khao Sam Roi Yot ("Mountain of Three Hundred Peaks") National Park, 23 kilometres south of Hua Hin, is a maze of lakes, limestone spires and mangroves. I take the jungle path to its most visited spot, Phraya Nakhon Cave, where King Rama V meditated in 1890. You can see where he signed the wall, as did Rama VII in 1926. The cave's delicate, sun-lit central pavilion is said to be the smallest temple in Thailand.

Khao Sam Roi Yot ("Mountain of Three Hundred Peaks") National Park, 23 kilometres south of Hua Hin, is a maze of lakes, limestone spires and mangroves. I take the jungle path to its most visited spot, Phraya Nakhon Cave, where King Rama V meditated in 1890. You can see where he signed the wall, as did Rama VII in 1926. The cave's delicate, sun-lit central pavilion is said to be the smallest temple in Thailand.

Khao Sam Roi Yot ("Mountain of Three Hundred Peaks") National Park, 23 kilometres south of Hua Hin, is a maze of lakes, limestone spires and mangroves. I take the jungle path to its most visited spot, Phraya Nakhon Cave, where King Rama V meditated in 1890. You can see where he signed the wall, as did Rama VII in 1926. The cave's delicate, sun-lit central pavilion is said to be the smallest temple in Thailand.

Despite its prominence, Hua Hin isn't the capital of Prachuap Khiri Khan province. That honour goes to the town of the same name - known simply as Prachuap - 90 kilometres further south. Its SEO-worthy motto, "City of pure gold, delectable coconuts and pineapples, delightful beaches, mountain and caves, land of spiritual beauty", is description enough. The postcard-perfect Ao Manao - "Lime Bay" - just south of town is one of the most beautiful beaches on the coast. It sits within the Royal Thai Air Force Wing Five base but is open to the public. Rent a bike in town to reach it. Having cycled across the runway, you're greeted by a troop of resident langur monkeys who, with punk Einstein hairdos and white, fur-framed eyes, gently cadge bananas and pose for photos. Thai troops battled here against Japanese forces in 1941, a prelude to the country's war-time occupation.

At Waghor, about 12 kilometres south of Prachuap city centre, is King Mongkut Memorial Park, a science and technology centre dedicated to the forward-thinking King Rama IV, who ruled from 1851 to 1868. Its tropical aquarium pulses with electric eels, Siamese tiger fish and turtles, while rays and sharks cavort above you in a walk-though tunnel. Check out the observatory and train museum, too.

"I've never heard of it," is the near-universal response from Thais when I mention the Royal Coast. More know about its little whistle-stop, Wang Duan, and the sign declaring the "Narrowest [point] of Thailand, 10.96 kilometres", the distance from the Gulf to the Myanmar border. A few years ago I took a dog-leg route, west from the beach and uphill to the frontier. The actual walking distance is 13.4 kilometres - do it and you've walked across Thailand in half a day.

"I'm 40 degrees better-off here," Rolf, a long-stay Norwegian visitor, tells me. "It's 10 below in Oslo, but here I'm 30 above." Thailand's camino real thins-out around the seaside town of Baan Grood, 150 kilometres from Hua Hin, but good reasons to be here don't. The hilltop Buddhist temple Wat Thang Sai, built in 1996 for the 50th year of King Rama VI's reign, is spectacular even by Thailand's exuberant temple standards. Downhill in the snoozy beach town, defrosting Nordics pass their winters with leisurely cycling, dining and doorstop-sized novels.

The Buddha cautioned: "The beautiful chariots of kings wear out." Similarly, the royal riviera, after a 300-kilometre journey, fades near Chumphon. I quit early, heading offshore from Baan Grood to little Koh Talu, an island of palm trees galore but no princes or palaces. Still wondering why this Royal Coast is so undersung, I find graffitied on my bungalow wall not the answer but instead a right-royal pun: "I think, therefore Siam."

The writer travelled at his own expense