St Patrick’s Purgatory involves three days of fasting and prayers, while standing on sharpened rocks. It’s not for everyone, but there must be a reason why people return each year …

St Patrick’s Purgatory is the Ironman of Christian pilgrimages, a gruelling three days of fasting, sleep-deprivation, hypothermia-inducing temperatures and prayer that attracts the gnarliest, toughest of pilgrims.

The site, on Station Island in Lough Derg, County Donegal, receives 15,000 visitors a year, and despite the cold, hunger, midges and tedium, people rave about it, emerging rejuvenated. Only a few devout and determined visitors brave the pilgrimage itself, but the vast majority of those who do are return visitors.

Facebook Twitter Pinterest Kissing the cross at Station Island. Photograph: Alamy

Historically, the cave at St Patrick’s Purgatory was considered a turnstile to the Gates of Hell, where St Patrick is said to have witnessed the tortures of eternal damnation in the fifth century, and in 1148 Knight Owein is said to have been dragged into the Underworld by demons with iron hooks. During the Celtic Tiger boom years, from 1995 to 2000, numbers fell, as they did in the century when a Dutch monk complained to the Pope that no demons had attacked him during his visit, but the pilgrimage – which comes to an end on Friday, 15 August with the feast of the Assumption of Mary – is thriving again.

Pilgrims begin their ordeal by crossing the exposed waters of Lough Derg to Station Island, where they surrender their shoes and socks before starting the three-days of prayers and invocations. These are completed while standing, walking and kneeling at various sacred spots, both inside the basilica above the cave and outside on treacherous rocks that are regularly resharpened, so that they remain as jagged as ever.

Facebook Twitter Pinterest St Patrick’s Purgatory, Lough Derg, Donegal. Photograph: Lar Boland

Pilgrims fast from the midnight before arrival until midnight of the third day, apart from a daily snack of dry toast or oatcake and black tea or coffee. There is the added possibility of a cup of infamous Lough Derg broth: hot water flavoured with salt and pepper.

Anyone caught trying to sleep on the first night is prodded awake by fellow pilgrims, or the volunteer organisers – possibly the same people who sharpen the rocks.

The chorus of Our Fathers, Hail Marys and renunciations of “the World, the Flesh and the Devil” has eased a little in recent year as people opt for a more inward, Buddhism-lite style of retreat. It’s still remarkably social, though. Communal suffering is a great social lubricant, whether you find God or demons.