The ghost of a volcano, and the hill of St Patrick
Slemish is the ghost of a volcano. Geologists reckon that around sixty million years ago, when this whole corner of the world was tearing and erupting, molten rock rose through a vent here and set solid in the throat of it. That plug of hard dolerite was tougher than the ground around it, and as the softer land was worn back over the ages, the old core was left standing proud — the green dome you climb today. It's why Slemish sits alone above flat fields, with no range around it: it's the one bit that refused to wear away.
The other story is the one that made it famous. As the tradition goes, a teenage Patrick — not yet a saint, just a captured boy — was carried off from Britain by raiders and sold into slavery in Ireland, and spent about six years on these slopes minding sheep and pigs for his master. The story says it was here, alone on the cold hill, that he turned to faith, before eventually escaping and later returning to Ireland as a missionary. Whether the sums of history quite line up, no one can prove — but the tie is old and deeply held, and it's why, every 17 March, people climb Slemish in his memory.
You don't need the legend to feel it, though. Stand on the top with the wind coming off the fields, Lough Neagh silver to the west and the Antrim coast running away to the east, and a short, sweaty climb turns into one of the best half-hours you'll spend outdoors in this part of the country. Get the boots on, pick a good day, and go up.