Bull Rock is the second lighthouse to mark this corner of the Atlantic. The first stood on nearby Calf Rock, part of a quartet of rocks - Bull, Cow, Calf, and Heifer - that punctuates the sea off the western end of the Beara Peninsula. Captain J. Wolf had requested in March 1846 that a light be built on Bull Rock itself, but the commissioners chose Calf instead. George Halpin designed an iron tower; Henry Grissell of the Regent's Canal Iron Works in London fabricated it in 1861. The tower was completed in August 1864 and the light first turned on 30 June 1866. Six years later, additional strengthening was added at the base. None of it was enough. On 27 November 1881, in a fierce Atlantic storm, the iron tower snapped clean off just above the strengthened section. The keepers were not in the tower at the moment it broke - they were trapped on the rock for two weeks before the sea calmed enough to be rescued. A temporary light was set up on Dursey Island. The lesson was clear: cast iron and the Atlantic are not a long-term arrangement.

Approval finally came to build on Bull Rock itself - the original site Wolf had requested four decades earlier. Miners were landed on the rock and went to work with hand tools. They cut 300 steps from the landing up to the lighthouse site, flattened areas for construction, and hewed the keepers' quarters into the rock. The lighthouse was completed in 1888, and on 1 January 1889 the new light was turned on. The rock itself is small enough to walk across - 750 feet by 540 feet - and rises 305 feet to its summit. Buildings for the keepers were arranged on the more sheltered parts of the rock. They lived here, in shifts, for over a century. The fog warning was replaced by a siren on 1 April 1902, then discontinued on 17 May 1989. The light was upgraded to vapourised paraffin (an alcohol burner heating paraffin into a gas) on 28 June 1910, and to electric power on 21 August 1974. The keepers were finally removed and the light fully automated on 31 March 1991. Twenty-eight years later, on 6 October 2000, the light converted to solar power - the latest in a long sequence of energy sources moving steadily away from anything that required a human hand.

The lighthouse exists because ships were sinking on these rocks, but the rocks were a place in Irish imagination long before they became navigational hazards. In the mythology, Donn was the god of the dead, and Tech Duinn - the House of Donn - was where souls assembled. Bull Rock, with the natural tunnel running through it from one side to the other, was identified as that gathering point. The hole became known as the Entrance of the Underworld. It is the kind of feature that picks up a story whether or not you offer it one: a black archway in a black rock at the edge of the Atlantic, where the swell rushes through and seabirds nest in the side walls. Today the rock is uninhabited and cannot be landed on by tourists. Boat tours from Dursey or the mainland circle it instead, passing close enough to the hole to see the light coming through. The lighthouse itself stands above the cliff, white and squared off and very much built by people who had no opinion on Donn one way or the other.

Bull Rock sits four kilometres off Dursey Island and nine kilometres from the mainland. Dursey is itself an outpost - the only Irish island reached by cable car, with a population that has hovered in the single digits in recent years. The Beara Peninsula stretches east behind it, ending in the Caha and Slieve Miskish mountains. The Atlantic, here, has no obstructions all the way to America. Storms run unimpeded across thousands of kilometres of open water before they hit Bull Rock, which is why the first lighthouse on Calf Rock did not survive and why the second, built on stronger ground with better materials, has stood since the year Vincent van Gogh painted his bedroom in Arles. The light still flashes from its tower in a sequence visible from far out at sea. The keepers are gone. The 300 steps are still there. So is the hole.