On a clear day, an adventurer atop Mount Brandon can gaze into the Atlantic and see the rocky Three Sisters, the Skellig islands and other enticing glimmers on the horizon.

The Irish saint for whom the mountain is named did more than look. According to the Navigatio Sancti Brendani Abbatis (The Voyage of St. Brendan), the 6th century abbot set out in a leather-and-wood boat, with 17 other monks, to find the Promised Land in the West.

"Brothers, do not fear," said Brendan, in a text that may have been written as early as the year 800. "God is our helper, sailor and helmsman, and he guides us. Ship all the oars and the rudder. Just leave the sail spread and God will do as he wishes with his servants and their ship."

The rest is a long story, one that scholars have compared with the Odyssey and the storm-tossed travels of St. Paul. Today, some historians believe that Brendan's story is built on a framework of history, as well as spirituality. This has only added to the mystery surrounding the saint, whose feast day is May 16.

"Brendan is at the top of the Celtic canon, with Patrick and Columba," said composer Jeff Johnson, who has recorded two CDs blending jazz, rock, chant and the Navigatio. "But his story is more than just a good story. At some point you have to try to see yourself building that boat and getting in it and starting out on that voyage. ...

"That's when it hits you: A voyage to where?"

Anyone who wants to answer that question will need to study Celtic Christianity. But Catholic writer Connie Marshner warns that seekers should avoid the Celtic shelves in mall bookstores. A press release for one hot book captures the spirit of the current craze: "At a time when many people are seeking out traditional beliefs, but remain wary of overly confining disciplines, Celtic spirituality offers something for almost everyone."

"There are people out there selling this idea that the Celtic Christians were earthy, natural, free-spirited people who didn't care a lot about sin and doctrine and things like that," she said. "But if you read what the Celtic saints wrote or read about their lives, you quickly find out that just isn't true. They were very disciplined and very concerned about the sins of the flesh."

The Navigatio itself is built on monastic disciplines and a sense of mission. Monks didn't climb into tiny boats and brave the North Atlantic because they "wanted to get in touch with their inner feelings and find themselves," said Johnson. "They knew that other monks had made these kinds of journeys before. It was a leap of faith, but they knew what they were doing."

Two decades ago, scholar Tim Severin became convinced that they also knew where they were going. Following medieval designs, his team built a curragh out of Irish ash, covering the frame with 49 oak-bark-tanned ox hides laced with two miles of leather thongs. Then he made a 4,500-mile journey, hopping from island to island across the North Atlantic.

In "The Brendan Voyage," Severin notes that many details in the Navigatio are surprisingly accurate. The saint visits an island full of sheep, which sounds like the Faroe Islands, and sees a giant crystal pillar right where voyagers usually see icebergs. The boat is bombarded by burning rocks near the volcanoes of Iceland and encounters a dense cloud near the Promised Land, which may have been the fog zone at Newfoundland's Grand Banks.

But the big question remains: Why attempt this journey?

Brendan's monks were explorers, who expected to return from their journeys stronger and with lessons they could teach others, said Johnson. They also were missionaries who took incredible risks in an attempt to start monasteries, and the Christian communities that surrounded them, in the wild places on the edges of their world.

"The Brendan in that boat was a real person. He had his doubts and fears, like we do," said Johnson. "But it says a lot that we struggle to understand the kinds of disciplines that gave him the strength to do what he did. ... Maybe what the church needs today is more spiritual explorers. Maybe we need more monks."