The Poisoned Glen probably isn’t poisoned, and may never have been. The likeliest story behind the name is a translator’s slip: the Irish neamh (heaven) misread as nimhe (poison) by a 19th-century mapmaker, the mistake printed onto the Ordnance Survey and never corrected. An older legend blames the one-eyed giant Balor of Tory, killed here by his grandson Lughaidh, his eye’s poison splitting the rock as it fell. A third, quieter theory points to a toxic plant, Irish spurge, said to have grown here and since died out. Take your pick.
What isn’t in dispute is the setting: an ice-carved granite amphitheatre in the Derryveagh Mountains, just outside the Gaeltacht village of Dunlewey, with Errigal rising over it and the ruined Dunlewey Church standing pale at its mouth.
Walking into the glen
This is an out-and-back, not a neat loop, whatever some maps suggest: a rough path of about 4km round-trip that runs in along the valley floor beneath the crags and back the same way. It is genuinely wet underfoot, the ground turning to sucking bog after rain, so this is a boots-and-waterproofs walk best kept to a dry spell between May and September. The reward is the amphitheatre itself, bare granite closing in on three sides, quiet apart from the Cronaniv Burn.
The ruined church at the entrance is worth the pause. Built around 1830 in white marble quarried nearby, it was a Church of Ireland church raised as a memorial to James Russell, landlord of the Dunlewey estate; roofless now, its pale stone stands out sharply against the dark slopes behind it. Local lore adds a resident ghost, the green lady, if you’re inclined to look for her.
Climbing on Bearnas Buttress
The glen is one of Ireland’s original climbing grounds, with routes worked out here back in the 1950s and 60s. Bearnas Buttress, the great wall on the valley’s side, is reckoned the largest continuous rock face in Ireland and holds the country’s longest ice climb when winter obliges.
The catch is the aspect. The faces run north to north-west and get very little sun, so they need a long dry spell to come into condition; pick a crag straight after rain and you’ll be climbing wet granite. The quickest to dry is Ballaghageeha Buttress, high up at around 400m. If you’re not climbing yourself, it’s still worth craning up at the wall from the valley floor to take in the scale of it.
Getting there and practical notes
- Finding it: from the R251, about 2km east of the Dunlewey Centre turnoff, take the minor road down through Dunlewey, past the ruined church, to roadside parking at a hairpin bend where the path begins.
- Parking: it’s a small roadside lay-by and it fills fast on a fine weekend – come early, and don’t block the bend.
- On the ground: no toilets, no shop, no bins; take everything back out with you, and keep dogs off livestock and nesting birds.
- Weather: mountain conditions turn quickly and the mobile signal is patchy. Pack a shell and something to navigate with, and check Met Éireann before you set out.
Nearby
Errigal itself is right on the doorstep, the quartzite cone you’ll have been looking at the whole walk, and the glen runs on toward Glenveagh National Park to the east. Down by the entrance, the Poison Glen viewpoint (spelled without the ‘ed’ on the signs) gives an easy roadside look over Dunlewey Lough and Lough Nacung. The valley has crept into Irish music too: Clannad put a track called ‘Poison Glen’ on Anam in 1990, and Altan named a whole 2015 album Gleann Nimhe – The Poison Glen after it.