Bhutan, the kingdom.

A dzong is a fortress and a monastery at once. Every district has one, and it is usually the largest building in its valley: a long whitewashed wall, a broad band of vermilion timber across it, small dark windows, and a gilded ridge above. Inside, a courtyard where the district's monks live and its administration still sits.

A dzong was built to be the last place to fall. The walls lean inward, the way in is one narrow gate, and the watchtower, the ta dzong, held the water. In the seventeenth century Zhabdrung Ngawang Namgyal raised them across the country as refuges and strongholds of the Drukpa faith. Several are still in use as both, and one, the ta dzong above Paro, became the National Museum.

When you visit one, you are entering a working place of worship, not a monument. Cover your shoulders and knees, take off your hat, and walk clockwise once you are inside.

Once a year a dzong courtyard fills with a festival called a tsechu, held on the tenth day of a Bhutanese lunar month to honour Guru Rinpoche, Padmasambhava, who brought Vajrayana Buddhism to the Himalayas in the eighth century.

The centre of it is cham: masked dance, performed by monks and lay dancers in brocade and painted wooden masks, telling stories that are part blessing and part instruction. Around them whole families sit on the flagstones for the day, dressed in their best. On the final dawn a giant appliqued thangka, a thongdrel, is unrolled, and it is said that to see it clears a lifetime of ill.

The dates follow the lunar calendar, so they shift a little each year. These are the months the big ones usually fall in.

• January to MarchPunakha Drubchen and Punakha TsechuThe oldest of the great tsechus, in the winter capital's dzong.
• March to AprilParo TsechuIn the courtyard of Paro Dzong, and one of the best attended.
• June to JulyNimalung and Kurjey TsechuIn the Bumthang valleys, gentler and less crowded.
• September to OctoberThimphu TsechuThe capital's own, with Wangdue Phodrang and Gangtey.
• November to DecemberJambay Lhakhang DrupWith the tsechus of Mongar, Trashigang and Trongsa, and Dochula.

Strung across ridges, passes, bridges and the roofs of houses, prayer flags are not decoration. They are lung ta, wind horse: printed with prayers and mantras and hoisted to let the wind carry the blessings out across the world.

They come in five colours, and the order is never random. Blue for the sky and space, white for the air and the wind, red for fire, green for water and yellow for the earth. The traditional prints are woodblock, and both ink and cloth fade in the weather, which is the point: the prayers are released as the flag wears away. Old flags are left to the elements rather than taken down.

You will see them at their thickest on the high passes. If you are crossing one, you can add a flag of your own.

Archery is the national sport, and a match is a social event as much as a competition. Two teams face each other down a range that is traditionally about 145 metres long, an enormous distance for a wooden bow, with a slim wooden target at each far end.

The bows are made of bamboo, strung taut and drawn to the ear, and a shooter may hold only one arrow in the air at a time. The opposing team does the scoring, and it is loud: when a man hits, his teammates sing and dance down the range behind him, and the women of the team answer from the line. The winning team is expected to host the other for a meal afterwards.

At the big ranges in Thimphu the equipment is modern now, compound bows and carbon arrows. The songs, the teasing and the celebration are exactly as they always were.

Bhutan rises from about 100 metres above sea level on its southern border to Gangkhar Puensum at 7,570 metres: the highest mountain in the country, and the highest unclimbed mountain in the world. Climbing it is not permitted, and neither is any peak above 6,000 metres, because the high mountains here are held sacred.

The country runs in bands: the narrow subtropical plains in the south, the central valleys where most people live, and the high Himalayas along the north, where the passes cross at well over 3,000 metres.

The takin, the national animal, is a shaggy goat antelope that looks assembled from spare parts, and lives mostly in the high forests. The raven is the national bird. The blue poppy, the national flower, shows for a few weeks in the alpine meadows and almost nowhere else.