Slemish is an isolated volcanic plug rising about 437 metres from the flat farmland of the Antrim plateau, some nine kilometres southeast of Ballymena. The cone is unmistakable on the horizon — abrupt, steep-sided, and quite unlike anything else in the surrounding landscape. Geologically it's the eroded neck of an ancient volcano, left standing after the softer rock around it was worn away.
What makes Slemish genuinely compelling is its connection to St Patrick. According to tradition, the teenage Patrick — captured from Britain and sold into slavery — worked as a shepherd on these slopes for six years in the early fifth century before escaping and eventually returning to Ireland as a missionary. The historicity of that claim is uncertain, but the association is old and the site has been a place of pilgrimage for centuries. Walking up it, looking out over the broad flat fields in every direction, it's not hard to imagine the isolation of that existence.
The walk to the summit is steep but short — the climb takes around 20 to 30 minutes from the car park at the base. The path is rough in places and decent footwear is worthwhile. The view from the top reaches across the Antrim plateau to the coast on a clear day. On St Patrick's Day (17 March) the mountain draws thousands of pilgrims, which can be a memorable spectacle or a reason to visit on any other day, depending on your preference.