As the largest and most famous monastery in Bulgaria, and also a UNESCO World Heritage Site, Rila Monastery can appear a little overwhelming if you visit in high season or during major Christian festivals. The crowds that gather in the picturesque yard, with its toy-like painted church and the striped arches of the galleries, can obliterate any feeling of holiness, or the tranquility that is usually associated with a monastic institution of such fame.

Visit Rila Monastery in winter, however, and you will be in for a completely different experience. The crowds of visitors are no more than a trickle, and the snow on the roofs and the nearby mountains transforms the compound into what could be the setting for a fairy story with a slightly ominous tinge. The fortress-like appearance of the outer walls, the cosy wooden-beamed balconies and the colourful, gleaming church, with the mystic slopes of the Rila mountains rising in the background, invite you to extend your stay as long as possible.

You can actually do this. The monastery offers good, cheap accommodation on site, which allows you to immerse yourself in its atmosphere as no ordinary tourist could: with the chime of the bells measuring time and the procession of black-clad monks heading to church.

You will also have time to learn more about this fascinating place.

For centuries Rila Monastery has been a treasure trove. Its mighty walls were built to protect its riches, and medieval Bulgarian kings and wealthy Bulgarians made lavish donations. The main church, Nativity of the Mother of God, was painted by the best artists of the 19th century.

Ironically, this place that has accumulated such earthly possessions was founded by a man who had absolutely no desire for strong walls, a treasury or the attention of the powerful.

St Ivan of Rila, who founded the holy abode, became its patron saint, and with time was accepted as the hallowed protector of all Bulgarians. He lived in the 9th-10th centuries, a fateful time. Bulgaria was then a mighty state, famous and feared as a result of the imperial and cultural policies of King Simeon the Great, but his constant wars had exhausted the country. When he was succeeded by his heir, King Petar, Bulgaria slid downhill. The poor became poorer, the rich got richer and the elite increasingly copied the lavish lifestyle of the archenemy, Byzantium.

The disappointment and dissatisfaction of ordinary Bulgarians were channelled into two spiritual movements, both of which cherished frugality and piety, and despised vanity and earthly possessions. They were, however, radically different from each other. The Bogomils were a dualistic sect that believed all earthly power, civil and religious, came from the Devil, and the only way to avoid damnation was to abandon traditional society and live in poverty in simple communities. The ascetic movement did not object to the social order: its adherents just chose to live in solitude in some deserted place, alone with their prayers. This explains why, when both state and Church persecuted the Bogomils as heretics, the hermits were not only left alone but were venerated as spiritual leaders.

Ivan of Rila was one such man. Born a humble villager, he led an ordinary life until his parents died, when he was 25 years old. Ivan then gave up all his property and became a monk, eventually ending up alone in the high and deserted Rila mountains. The fame of his piety grew and spread far and wide, and even King Petar visited him. Ivan of Rila would not agree to meet the king and only showed himself from a distance. Of all the lavish presents that Petar had brought, he accepted only some fruit, refusing the gold.

Adam and Eve as seen by a 19th century Bulgarian icon painter

Even in the 10th century living a simple life far from crowds was not easy. Before long the hermit found himself amid a growing community of followers, and was forced to seek solitude farther up the mountain. There he died, supposedly in 946, at the age of 70. Today a small chapel marks the place where he lived. The monastic community that sprang up around his initial place of habitation became Rila Monastery.

The hermit was canonised soon after his death, and in the following centuries his supposedly miraculous remains travelled around Bulgaria. In the 1180s they were notoriously stolen during a Hungarian raid and brought to what would later become Budapest. Subsequently, the bones ended up in Tarnovo and were only returned to their rightful home, with much pomp and ceremony, as late as 1469. They are now in the monastery's main church, exhibited for veneration in an elaborate wooden reliquary that is opened only on high days.

Rila Monastery monks led by their abbot perform vespers

Ivan of Rila is said to have subsisted on a diet of herbs and potions to embalm himself while he was still alive. Some stories depict him as notoriously bad-tempered. He would curse whole villages for refusing to give him food or shelter, and was responsible for the death of his young nephew. The boy had decided to become a monk and joined Ivan. When the angry father reclaimed his son, Ivan of Rila asked god to save the young boy from the woes of earthly life. The nephew never reached home, as he was bitten by a snake and died on the way back.

The veneration of St Ivan of Rila passed down through the centuries, attracting a never-ending stream of donations to Rila, until it grew to be the largest monastic foundation in Bulgaria.

The earliest surviving building is Hrelyu's Tower, a defensive structure with its own small chapel, built in 1335 by a local lord to provide shelter for the monks. The 23-metre-high tower proved useful during a number of bandit raids when Bulgaria was under Ottoman rule. In more peaceful times it was used as a prison, and as an isolation ward for sick or deranged monks. For the modern visitor the most alluring feature of Hrelyu's Tower is the medieval murals in the 5th floor chapel. The two-storey belfry adjacent to the façade dates from the 19th century.

The rest of the monastery may have been impressive and beautiful, but it was destroyed in a devastating fire in 1778. Restoration took several decades, during which time, in 1833, a section of the new building was lost to another fire.

It was during the 1830s-1850s that the strong walls which now protect the monastery and the living quarters appeared, soon to be complemented by the striped galleries and the exquisite main church covered both inside and out with frescoes shining blue, green, red and yellow. Its architecture is a major deviation from the prevalent Bulgarian Revival Period style of the day. Built on the site of an older, medieval basilica, it copied the style of churches on Mount Athos, with a cross-shaped nave, five domes and a colonnaded outside gallery instead of a narthex.

Resting place of famous Irish journalist James Bourchier (1850-1920). Bourchier spent many years in Bulgaria and chose to be buried near Rila Monastery

The Rila Monastery library preserves books and manuscripts from the 11th-19th centuries, including the precious Rila Charter, issued by King Ivan Shishman in 1378, which still bears his gold seal. The document specifies the properties of the monastery and how it should be run, making it an important historical source about life in the 14th century.

A more sinister story can be found inside the church. In the misty light of one of the side aisles, a simple cross marks the resting place of King Boris III (1918-1943). Bulgaria's last ruling monarch died soon after he returned from a meeting with Hitler in Germany. He was buried at Rila Monastery, but his remains did not stay there for long. Fearing his grave might become a place of pilgrimage, the Communists exhumed his corpse in 1946, and reburied it several times in different places. What actually happened to the king's remains in the end is a matter of continuing speculation, but after the collapse of Communism, in 1989, only his embalmed heart could be found. It was reburied at Rila Monastery in 1993.

Another man of prominence in Bulgarian history was buried close to the monastery. James Bourchier (1850-1920), the Irish journalist who covered Bulgaria's tumultuous history in the late 19th and early 20th centuries, chose to remain in Bulgaria even in death.

The cultural and historical significance of Rila Monastery ensured that even under Communism it continued to be viewed with respect. It was maintained and treated as a place to take visitors on bus tours, as described by John Updike, who visited in 1964.

In 1961, Rila Monastery was declared a state museum; religious activity declined, and the monastic community shrank to just a few dozen.

In 1976, the whole area was declared a national historical reserve, and the Monastery was listed as an UNESCO World Heritage site in 1983.

There are several churches and other religious sites around Rila Monastery. The Presentation of the Virgin Mary Church in the monastic cemetery has 19th century murals and an ossuary. Three miles beyond the monastery stands the Old Fasting House, supposedly the original place where St Ivan of Rila was buried. In 1820, a church, The Dormition of St Ivan of Rila, was erected on the site. A new fasting house marks the burial place of the saint's nephew. Two churches stand there: the 18th century St Luke's possessed such a fine iconostasis that it was taken away and can now be seen in the National History Museum, while the church of the Intercession of the Mother of God dates back to the beginning of the 19th century. On the way to the Old Fasting House there is a newer church, St Theodosius of Tarnovo. Building started in 1956, but ground to a halt under the Communist government and it remains uncompleted.