Splashed across the exterior of a farmhouse is an image I never expected to see on public display – let alone in a Buddhist country. Sandwiched between a crouching tiger and a leaping dragon, an enormous phallus and its accoutrements squats below a wooden lattice window frame.

Cartoonish in nature, it could be mistaken for a piece of profane graffiti. But the unusual mural, I later learn, belongs to one of Bhutan’s most renowned Buddhist teachers. Found in temples, souvenir stalls and dangling from the rear-view mirror of buses, the unconventional piece of religious iconography is a symbol of good luck. Still, that doesn’t stop me (or even my Bhutanese guide) from sniggering every time I see one.

Then again, it’s hard not to smile in one of the world’s most mystifying and charismatic countries, a utopian mountain kingdom where GDP has been ditched in favour of Gross National Happiness as a measure for charting the country’s development.

First open to tourists in 1974, this hidden Himalayan Kingdom – which sits between India and China – has attracted a steady stream of curious visitors intrigued by the country’s strong spiritual beliefs, social cohesion and fondness for outlandish, folkloric tales.

Now there’s even more reason to explore Bhutan’s steep mountains and deep valleys, with the launch of a new pilgrimage trail.

A pathway to greatness

Once used by Himalayan traders and garps (royal messengers) in the 16th century, a network of trails connected the country from east to west, providing a means of communication which played an important role in the unification of Bhutan in 1907. When roads arrived in the 1960s, these trails fell out of use. But an ambitious project instigated by Bhutan’s King Jigme Khesar Namgyel Wangchuck – also a keen hiker – has been undertaken to repair and restore these historic routes.

“I think this may be the greatest, long-distance trail in the world,” says Sam Blyth, co-founder and chair of charity the Bhutan Canada Foundation, who worked alongside the Royal Bhutanese Government and the Tourism Council of Bhutan to complete the new 403km Trans Bhutan trail.

When we meet at the Khang Residency hotel in Bhutan’s surprisingly modern capital Thimphu, Sam speaks enthusiastically about an ancient network of pathways he’d heard about 40 years ago and always dreamed of walking.

“There’s not another country in the world where you could build a 400km trail in three years,” he enthuses, praising the 1,000-strong team of Bhutanese DeSuung members (a voluntary organisation empowering unemployed people to become guardians of the peace) who “hand-cut 10,000 stone steps and built 18 bridges”.

Retracing history

It would take around 30 days to do the full trail, but tour operator G Adventures has condensed some of the best sections into an escorted group tour led by Dorji Bidha, one of Bhutan’s few female guides.

“My grandparents met each other crossing these valleys,” says the petite 32-year-old, who has temporarily swapped her national dress of a kira (a wraparound robe) for hiking gear and a machete slung loosely around her waist. “My grandfather would bring meat, cheese and butter to barter for rice.”

Our first 13km trek begins 3,000 metres above sea level at the Dochula Pass, an historic crossroads where 108 memorial stones – known as chortens – commemorate soldiers killed in a 2003 conflict with Indian insurgents.

Downhill all the way, I step over thick carpets of moss sprouting with mushrooms and wander through tunnels of twisted hemlock trees draped in garlands of lichens. Dressed in orange boiler suits, volunteers from the DeSuung are pulling back branches to keep paths clear – a job, I suspect, which will keep them busy for some time.

Almost 70% of Bhutan is covered in forest, providing a haven for Bengal tigers, black bears and takins (an oddly put together animal resembling an antelope and a goat). In a brave move, authorities recently introduced a controversial daily tourism levy of $200USD per person to bolster sustainable development. The only country in the world to confidently declare itself carbon negative, it’s a place where nature remains a priority.

Throughout our week of treks, the only dangerous creatures we encounter are needle-thin leeches who have a talent for wriggling into my hiking boots. But stories of flying monks and cannibalistic demonesses are enough to keep dreams dramatic during a night spent camping on valley slopes, metres away from a gushing river swollen with monsoon rain.

Although endless stretches of fairy-tale scenery are a big selling point for the Trans Bhutan trail, community encounters and an opportunity to learn about myths and legends is just as important. I exchange smiles with elderly women spinning prayer wheels outside temples, share lunch with a family sat cross-legged in a farmhouse, and receive a blessing at a shrine set below a weeping cypress tree in the playground of a remote primary school.

A temple in the sky

Several temples and dzongs can be found along the Trans-Bhutan trail, but one of the country’s most iconic religious sites requires a small, worthwhile detour. Carved into a sheer rockface overlooking Paro, the Tiger’s Nest monastery is an architectural marvel and UNESCO World Heritage Site. Within easy reach of Paro airport, it’s a trip I manage to squeeze in before making the long journey home.

Winding through forests where hydro-powered prayer wheels chime and prayer flags flutter in the breeze, we climb steep pathways and hundreds of steps to reach the complex. Wrapped in maroon robes, young monks scurry between prayer rooms, disappearing into wafts of incense smoke. Far from the roar of traffic and hum of mobile ringtones, they practise traditions cherished for hundreds of years.

In the five centuries  since trails were first built in Bhutan, the country has changed dramatically, but there’s still a deep respect for the past. In decades to come, I’ve no doubt valleys will still be smothered in forests, candles will continue to burn in precipitous temples, while the power – and comedy value – of the phallus won’t diminish one little bit.

How to plan your trip

G Adventures (gadventures.com; 020 7313 6953) offers an 11-day escorted Camp the Trans Bhutan Trail itinerary for £3,449pp, including a mixture of camping, hotels and homestays, and the daily Sustainable Development fee. International flights extra.