Carn Eighe () is a mountain in the Northwest Highlands of Scotland. Rising to above sea level, it is the highest mountain in Scotland north of the Great Glen, the twelfth-highest in the British Isles, and, in terms of relative height (topographic prominence), it is the second-tallest mountain in the British Isles after Ben Nevis (its "parent peak" for determination of topographic prominence). Carn Eighe lies between Glen Affric and Loch Mullardoch, and is at the heart of a massif along with its twin peak, the Mam Sodhail.
Administratively, it is in the Highland council area, on the boundary between the historic counties of Inverness and Ross and Cromarty, on the former lands of the Clan Chisholm. The mountain is not easy to access, being from the nearest road. Another prominent peak to the north, Beinn Fhionnlaidh, is even less accessible.
Name
The name "Carn Eighe", formerly spelled "Carn Eige" on Ordnance Survey maps, comes from Scottish Gaelic and has been interpreted as meaning "file peak" or "notch hill". However, according to Ainmean-Àite na h-Alba, the original Gaelic name is Càrn Èite.
Landscape
The summit is pyramid-shaped, the culmination of three ridges meeting. The nearest Munro is its "twin summit", Mam Sodhail, about to the southwest, and there are three other Munros on the massif. Beinn Fhionnlaidh ends a spur to the north, and there is a much longer grassy ridge running out to the east, which after leads to Tom a' Choinnich () and then after a similar distance culminates in the rather bland summit of Toll Creagach, at . The full set of Munros has been "completed" at least 6,000 times since then.
Flora and fauna
Typical of the Scottish Highlands, the slopes of the mountain are largely treeless, especially at higher elevations. The mountain is instead clad in a variety of grasses and mosses, which towards the summit are covered by snow during parts of the year. The lower slopes are described by Muir as "boggy, sodden moorland". The base of the southern side of the mountain, adjacent to Loch Affric, is wooded with Scots pine interspersed with other species such as oak, birch, and beech. These woods are inhabited by a number of endemic fauna, including the crested tit and the Scottish crossbill.
Location
Situated in the north of Scotland, Càrn Eighe is on the border of two historic counties, Inverness and Ross and Cromarty, and is the highest point of the latter. The mountain is fairly remote, more than from the nearest road, in Glen Affric, although there is a youth hostel (Alltbeithe) in the same valley that is nearer. The summit is at UK grid reference NH123261, which falls on the OS Landranger 25 map, the OS Explorer series 414–5, and the much larger area map 9.
Climbing
The mountain can be climbed from the south, beginning at Loch Affric, up the north side of Gleann nam Fiadh (fording a stream) and reaching the summit of both Càrn Eighe itself and then Mam Sodhail in either clockwise or anticlockwise fashion (route described anticlockwise), potentially including Beinn Fhionnlaidh as an extra, since this is relatively difficult to access in any other way.