Its tail sways with the seasons, they say, wagging to the north with the summer’s southern swells, and then back when the currents reverse in winter. And from its head, sulphurous steam jets out of volcanic vents in spots where one might expect to find nostrils.

I’m heading for Turtle Island on the foredeck of a 29-foot ocean cruiser, skipping over small swells. There is an exhilaration to any ocean voyage in fair weather, and all six of us on board are smiling.

Tourists have been taking pleasure cruises to Turtle Island, which lies 10km off Toucheng, since at the latest the 1930s, but a lengthy hiatus came with World War II and then a nearly 40-year moratorium on coastal tourism under Chiang Kai-shek’s martial law.

Now Toucheng – gateway to the beaches of the Lanyang Plain – has become something of a boomtown. Since 2020, the beaches up and down the coast here have ranked as the most popular for Taipei day trippers and second most popular in all of Taiwan, with more than 1.3 million visitors per year, according to Taiwan’s Ministry of Tourism.

During the summer season, from April to October, as many as 1,800 people leave the town’s Wushi Harbour each day to visit Turtle Island. Meanwhile, yachts – such as the one I’m on – take smaller groups to anchor offshore for watersports, barbecues and even the occasional proposal of marriage.

Unlike Taiwan’s other coastal destinations, where a dogmatic faith has been placed in luxury resorts, a hipster surf crowd has been in the vanguard of development north of Wushi Harbour for two decades, affecting transformations with brightly painted surf shops, repurposed hipster B&Bs, “vanlife” hashtags and nut-brown suntans.

In Toucheng itself, though, holiday apartment towers have been springing up (many are listed on Airbnb) and a growing population of city folk now treat the town as a suburb – the commute to Taipei can be as quick as 45 minutes.

Toucheng was established around 1800 at the first safe anchorage for ships coming down the treacherous, rocky coast from Keelung, on Taiwan’s north coast. Its name literally means “first city”, and subsequent settlements to the south were named Ercheng (“second city”), Sancheng (“third city”), Sicheng (“fourth city”) and so on.

Toucheng quickly established itself as a trading hub, with access to the rich farmland of the alluvial flats of the Lanyang Plain, which is ringed by mountains that were then difficult to cross.

Toucheng remained the most important trading port on Taiwan’s east coast for the entire 19th century. This history can be seen on Toucheng’s Old Street, a quaint alley hidden in the midst of an otherwise industrial country town.

The street is lined with elegant, colonnaded brick buildings, many dating from its days as a bustling harbourfront and others from the 1920s Japanese colonial era.

By 1812, Qing officials had established a yamen, or government office, in Toucheng, to oversee trade and collect import duties. In 1826, Wushi Harbour was officially opened to overseas trade, attracting Chinese ships from ports stretching from Hainan to Jiangsu.

American and European square-rigger ships called here, and excavations of Qing-era sites have uncovered tens of thousands of diamond-shaped objects made of a Mediterranean shell material.

“We’re not sure exactly what they were, but it’s believed they came here as ballast,” explains Kang Bao-yu, the 63-year-old proprietor of Heping Street House, a shop in a one-storey brick building on Toucheng’s Old Street that sells curios, used books and Chinese tea.

Kang, a local heritage advocate and the granddaughter of the painter and calligrapher Kang Yan-quan, tells me of a poem, Sail Shadows, that was composed in 1938 and encapsulated the image of the port in its heyday:

Springtime brings ten-thousand sails to Wushi/In the autumnal beauty of this placid inlet, sail shadows ripple in the waves below.

“This poem used to hang on the walls of nearly every household in Toucheng,” claims Kang.

Near her shop is the port’s old customs warehouse, the Shisanhang, or “the 13 hongs”, the same name used for the trading zone for tea and opium in 19th century Canton.

“Shisanhang was a kind of generic name used for exterior trade zones in ports throughout China during the 19th century,” explains Chen Bi-lin, director of Toucheng’s Lanyang Museum.

Kang explains that “the only reason [the Shisanhang in Toucheng is] still standing is because they built the walls too thick so nobody could tear it down”. The long, low building, now a private residence, has been lovingly restored with a roof of black ceramic tiles and a facade of cedar slats.

Toucheng’s cosmopolitan glory faded with the end of the maritime era. The river began silting up from the late 19th century onwards and a railroad was constructed in the 1920s.

Behind the old riverfront lies a pond about the size of a football pitch, a vestige of a watercourse that once was connected to Wushi Harbour, which is about 1km away and now the preserve of fishermen and tourists.

As our boat skirts its towering cliffs, we learn that in geological terms, Turtle Island is surprisingly young. The first of its twin peaks burst out of the sea around 7,000 years ago, the southernmost volcano in a “chain of fire” that arcs through the Okinawan islands to southern Japan.

The most recent major eruption occurred 3,600 years ago, although minor seismic events have taken place as recently as 1944.

Like most boat tours around the island, ours begins with a visit to the Milk Sea, near the Turtle’s head, where undersea vents shoot superheated water from the ocean floor, producing billows at the surface that range from milky white to an opaque, brilliant turquoise.

“You can take photos of people free-diving there, and it looks like they’re swimming in the sky,” explains Lin Chih-chau, who runs tours through his company, Blue Bay Travel.

On a later trip, to the island itself, captain Liu Hou-han says that most sailors prefer to call the Milk Sea the Yin Yang Sea, after the Taoist diagram that mixes black and white.

Liu, 64, sprightly and silver-haired, was one of the last residents of Turtle Island and describes his childhood there as having been “extremely poor”.

“We had nothing. We could grow sweet potatoes in terraces on the mountain, but we couldn’t even grow rice.”

The island’s fishing settlement dates back to at least 1840, as estimated from the island’s oldest grave, and was carved out from jungle on the island’s only flat area, the Turtle’s tail.

In 1977, the government removed the 700 residents to the Taiwanese mainland. The island was used as a military base between 1978 and 2000, by which time “its value for tourism outweighed its military value”, explains Liu.

Having landed, our captain and guide leads us up 1,700 stone steps to the volcano’s 398-metre (1,300 foot) peak.

Barely breaking a sweat, he points out profusions of broad-leafed edible taro plants, sweet-nectared hibiscus – “when I was a child, we didn’t have candy, just these”, he grins – and growths of rattan that teachers once used to discipline their students.

The peak, capped by a two-storey viewing platform, offers a majestic perspective, staring down the blazing green slopes of a conical mountain surrounded by azure waters – to the east, the cerulean drifts of the Milk Sea and the Pacific, to the west, the escarpment of the Taiwanese coast.

Liu guides us back down and through the remains of the abandoned village, where only a junior school and a couple of stone, thatched-roof houses survived the army’s bulldozing of 1978.

Beyond these lonely ruins, we enter military tunnels blasted 800 metres into the volcano’s cliffs. In a gun emplacement, we find a defunct Howitzer standing sentry over an implacably serene view of the Lanyang Plain.

Off the tip of the Turtle’s tail, a small fleet of gleaming white yachts have anchored, their passengers diving, paddle boarding and bobbing on the enticing, blue waters on inflatable unicorns.