Irish playwright George Bernard Shaw described Skellig Michael as "the most fantastic and impossible rock in the world." The tiny island, which bursts out of the Atlantic like a sandstone pyramid, welcomed a group of ascetic monks back in the sixth century, and the rugged path they cut around the jagged coast now attracts trekkers by billing itself – quite rightly – as Ireland's most spectacular and treacherous walking trail.

Adventurers set sail from the harbor of Portmagee, a pub-peppered fishing village on the coast of County Kerry. Because the island is both a UNESCO site and a wildlife sanctuary, boat trips are strictly marshaled and only 300 passes are granted daily from the likes of local skipper Joe Roddy.

From port, it's a 45-minute trip across the bracing, salty surf of the North Atlantic. As the mainland folds into the distance, first sight is Little Skellig (the smaller of the two Skelligs), a haven for gray seals and home to one of the largest gannet colonies in the world. This crag is off-limits to visitors, but the birds make for a dramatic sight: Flocks plunge into the ocean like aerial torpedoes and pop up snapping whole schools of fish.

Forgiving tides and swells lead to Skellig Michael, eight miles from the mainland. The cacophonic squawk of bird life choruses around the pier as visitors disembark. Razorbills and guillemots dot the cliff face, while teary-eyed puffins clumsily swag around the island with a Galapagos-worthy sense of fearlessness.

From the jetty cove, a wide path kisses the cliffs until reaching the base of the man-made mountain stairway. It's best to stretch those sea legs before venturing any farther: 618 rickety steps, carved out of the bare rock, can be tough on the quads. This gruelling, medieval stairmaster coils up 600 feet, offering hikers a number of chances to fall to their doom. There have been fatalities over the years, but Irish authorities have blackballed the suggestion of safety fences in order to protect the site's sanctity.

Hikers who reach the summit's hermitage (most do) find a remarkably intact monastery of ancient beehive huts. Because boats are only permitted a few hours on the island, it's best to eke out a panoramic perch, simply hang on to the moment of extreme isolation, and take in the view from the very edge of the Celtic world.

More information: Portmagee lies a four-and-a-half-hour drive from Dublin City. Ferry rides to Skellig Michael typically cost $60 round-trip, and there is no entrance fee to the island.