Round Island is a 35-metre hump of Hercynian granite rising at the northern edge of the Scilly archipelago, three miles from St Mary's and just north of St Helen's. The Cornish name for it translates as the hump lighthouse, and that is exactly what was built on top in 1887. William Tregarthen Douglass - chief engineer for the Commissioners of Irish Lights and a member of a famous family of British lighthouse engineers - designed the 19-metre ashlar granite tower for Trinity House. At the time of its building, it was one of only three lights in Scilly, alongside Bishop Rock to the west and St Agnes to the south, each marking a different approach through the rocks. Round Island guarded the northern threshold. Its first flash crossed the Atlantic on 12 November 1887.

Getting men and stone onto Round Island was its own engineering problem. There is no harbour, no beach, nothing but vertical granite walls dropping into deep water. Workers cut a flight of steps up the south face of the rock, and supplies were hauled up the cliff by an aerial cableway from a small landing. Inside the lighthouse walls the keepers tended a tiny vegetable garden, every spoonful of soil shipped in from somewhere else. The first optic was extraordinary: a biform hyperradial lens 4.6 metres tall, weighing over eight tons, built by Chance Brothers of Birmingham. To distinguish it from a similar lens at nearby Bishop Rock, Round Island's lamp showed a single red flash every thirty seconds - tinted glass dimmed the light, so engineers fitted oversized ten-wick burners to push it back through the colour. In 1912 a pair of huge red Rayleigh trumpets were mounted on a fog horn house alongside, blasting four notes every two minutes through the Atlantic murk.

The light was electrified in 1966 and a helicopter pad was built on the rock in 1969, ending the cliff climb forever. Trinity House automated the lighthouse in 1987, and the last keeper turned off the kettle for good. Most of what they had brought with them - cats, rats, vegetable patches, oil-soaked rags - either left or had to be removed. The island was designated a Site of Special Scientific Interest in 1995 and is now managed by the Isles of Scilly Wildlife Trust. The European storm-petrels the old keepers once mistook for a draft of feathers are back in force: the Seabird 2000 survey counted 183 occupied nests, and a 2006 follow-up found 251, the second-highest total in Scilly. Manx shearwaters breed in the cliffs too. A long campaign to eradicate the brown rats that had reached the rock - probably via the cableway baskets a century before - was completed in the early 2020s, and the seabirds have responded.

The original red flash was replaced long ago. The current lamp is a 360-millimetre revolving drum optic, upgraded to LED in 2025, throwing one white flash every ten seconds with an intensity of 42,945 candela and a range of 18 nautical miles. The tower itself is Grade II listed, and landing is forbidden except for maintenance. Approach Scilly from the north on a clear evening, by ferry or by air, and Round Island is the first thing that resolves out of the haze - a granite stub topped with a white drum, a horizontal flicker at the edge of the world. The puffins that workmen reported walking into their kitchens in 1887 are gone, lost to egg-collecting long before. The storm-petrels, smaller and more careful, are still here.