About 30,000 people flock every year to a windswept little Irish island to walk barefoot, eat one meal a day of black tea and oatcakes and then fast through an all-night vigil.

They are not masochistic tourists but Roman Catholics and others in need of spiritual sustenance who eagerly embark on a rigorous three-day penance, St. Patrick's Purgatory, which has been called the toughest pilgrimage in the world.

They come from as far away as California and Australia to Ireland's national shrine of pilgrimage at Lough Derg, where during the 11-week summer season of penance bishops rub shoulders with farmhands and bankers with dukes in this scenic corner of Donegal.

"When you take the shoes off someone, you take away the fac ade we all hide under," said Monsignor Gerard McSorley, prior of Lough Derg, which has been attracting pilgrims to its remote site in northwest Ireland since the 12th century.

Legend has it that Lough Derg was founded by St. Patrick, the patron saint of Ireland, who brought Christianity to the island in the 6th century and whose national day on March 17 is celebrated with boisterous big-band parades through dozens of Irish towns and villages.

"Lough Derg," which means "Red Lake" in Gaelic, commemorates the day when, according to legend, St. Patrick came to kill a serpent that had been terrorizing villagers. As its blood spilled out, the lake gained a name for posterity.

Today's pilgrims face a tough test of character and faith, with strict rules laid down for everyone who takes the motorboat across the choppy lake to Station Island, their bleak home for three grueling days.

All pilgrims must have fasted from the midnight before their arrival.

On reaching the dock, they go to the hospice, remove all footwear and begin the rounds of prayer at the various stations of the cross.

They spend the whole of the first night in a prayer vigil in the austere, green-roofed basilica and the second night they gratefully accept a "penitential bed" -- straw mattresses on bunk beds in the hospice.

No radios, televisions, cameras, alcohol or books are allowed on the island, a rocky little oasis of calm on a lake whose shores are fringed by heather-clad mountains.

"People come here for reasons that range from the frivolous to the serious -- getting through exams, praying for a sick brother or parent, even for the state of the nation or just to get a job," he said. "It is the toughest pilgrimage in the world and really harks back to St. Patrick's time. It is true to the spirituality of prayer and penance of the early monks."

Station Island, barely 400 yards wide, with its basilica and hospices with their spartan dormitories, is deserted for 41 weeks of the year. But for the summer season it is crammed with up to 800 visitors a day.

The pilgrimage, which costs less than $20, always proves to be a great leveler, and McSorley recalled how Britain's duke of Norfolk got "the same treatment as everyone else when he came here. That is what he wanted and what he got. Bishops are treated the same way, too." There are four priests working on the island full-time in the June-August pilgrimage season.

Such a steady flow of pilgrims to a remote corner of an island on the edge of Europe may appear to be a strange phenomenon in this age of ever-growing materialism in the Western world. But McSorley, who first visited Lough Derg when sent to the island at age 14 by his local priest, argued it is a necessary safety valve, particularly for the young.

For more information about Lough Derg and the pilgrimage, write: The Prior, St. Patrick's Purgatory, Lough Derg, Pettigo, Co. Donegal, Ireland.