But alongside detailed drawings of dragons and red-faced deities with snakes wound through their nostrils, I am surprised - stunned even - to find garishly graphic cartoon images of enormous three-metre willies.
Yes, that's right - big, throbbing male organs of the sort you might expect to find daubed on a schoolboy's pencil case.
Spouting and spurting, they float across facades like fat worms in crash helmets riding fur-trimmed Segways, and one joker has even scrawled "Wel-cum" across the doorway - all in delicate script, of course.
Sniggers aside, this is not some smutty attempt to entertain tourists; the phallus has great cultural significance for the Bhutanese.
"It belongs to the Mad Monk," explains my guide, 25-year-old Kinzang, as we walk towards the Chimi Lhakhang monastery, built in honour of the unorthodox 15th century wise man.
Also referred to as the "Saint of 5000 women" (for obvious reasons), he enlightened masses with his "thunderbolt of flaming wisdom", which has since become a talisman, mass produced as key rings, necklaces and even penis paperweights.
Couples struggling with fertility regularly visit the small wooden-and-stone structure just outside the country's former capital, Punakha, and Kinzang mischievously tells the tale of a Japanese tourist who gave birth to a child bearing a suspicious resemblance to a Bhutanese guide.
Such openness about sex and a willingness to crack crude jokes seems incongruous to the pious and disciplined Bhutan I had imagined, but humour, happiness and harmony lie at the heart of this Himalayan paradise.
This is, after all, the country where the only traffic light was ripped out for disturbing the peace and replaced with a "dancing policeman" who conducts cars with his white-gloved hands, as if they were musicians in a symphony orchestra.
Closed to the outside world for many years, this Buddhist mountain kingdom has been slowly opening up to tourism since 1974.
The process of opening up is a slow on. A mandatory daily tax, from $273 , covering food, accommodation, transport and licensed guides, helps keep the number of visitors at a sustainable level, but interest in the country is rapidly growing: in the past decade, visitor figures have jumped from 13,000 a year to 133,000, according to the Tourism Council of Bhutan.
I have joined a tour with adventure travel company Explore, travelling along bumpy roads subject to frequent closures, meaning journeys must be planned with military precision.
As we drive through chir pine forests festooned with prayer flags, stopping to admire the ruby-red rhododendron plants in bloom, I ask Kinzang how life has changed in the past few years. Technology has played a big role: the first TV sets arrived in 2001, and now most people have mobile phones and internet access.
"Before, it would take days to pass messages through the valleys," says Kinzang, who says he enjoys surfing the internet for updates on his favourite pop band, One Direction.
Remote communities still exist in Bhutan, but with the advance of electrical cables and tarmac comes inevitable Westernisation.
Religion forms the backbone of Bhutan, and temples, stupas and dzongs (fortresses) are staples on a visitor's itinerary.
Ornate paintings, silk banners and nightmare-inducing icons form a common theme.
Bhutan's most sacred site is the Tiger's Nest Monastery, lodged into a cliff face 900m above the Paro Valley.
"Every Bhutanese would like to come here at some point in their lifetime," says our older and more experienced guide, Singye.
Legend suggests Guru Rinpoche, who brought Buddhism to Bhutan, spent months here meditating in a cave after arriving on the back of a flying tiger. As we gather at the start of the tiring uphill trek, devotees are prostrating themselves in the dust.
A low population density - most of the 750,000 inhabitants live in valleys and on mountain slopes spread across 38,000sq/km - means Bhutan has plenty of space and resources available.
Provision of basic needs forms the foundation of GNH (gross national happiness), which the government famously uses to measure development in place of the gross domestic product popular elsewhere.
Driving distances are long in Bhutan, but watching the landscape change from snow-dusted mountains to misty, lichen-draped forests is mesmerising.
The final stop on our journey is Paro, where thousands have converged for a five-day festival, the most popular event in Bhutan's colourful calendar.
At 3am, we gather at the Rinpung Dzong, just in time to witness a grand procession. Led by a fanfare of pipes and bugles, monks buckle under the weight of the rolled-up, 45-metre Thangka tapestry, with crowds clamouring to touch the 18th century holy relic.
We sit on the whitewashed steps of an amphitheatre as the delicate silk banner is hoisted up and slowly unfurled, a bang of the gong marking each unravel. The chanting, bell-ringing and ceremonial blessings continue for almost five hours.
Once the stage is cleared, masked dances begin; a stream of terrifying deities bound athletically through the air and swirl like spinning tops, their embroidered skirts billowing in the warm wind. As the drumbeats intensify, the dancers' spirals become a blur, until open-armed assistants have to physically interrupt the trance-like spell.
Light relief is provided by a cast of comedy characters, who indulge in the sort of slapstick antics that would make Benny Hill blush. And the phallus is back, this time as a truncheon, wielded by a red devil and used to hit naughty children on the head.
The audience repeatedly guffaws loudly - including the Dragon King, King Jigme Khesar Namgyal Wangchuck who mingles freely in the front row with farmers and grubby-faced workmen. His father, the fourth King of Bhutan, celebrated his 60th birthday last year.
Ambitions are big for a country so small, but on this occasion - although the Mad Monk might disagree - size does not really matter.
There is one international airport, Paro, serviced by two airlines Drukair and Bhutan Airlines.
