There are a lot of mountains carrying the name Carn Dearg around Glen Nevis: the name means red hill, which is generic enough. The one in the picture is the south-western extreme of the Ben Nevis massif; there is another marked on the OS Explorer map to the north of it, over which you travel on the "tourist" track to the Ben. Carn Dearg also describes a route to Ben Nevis for experienced hillwalkers and mountaineers seeking more exhilaration and excitement; the views seen along the way are certainly more intriguing. This route starts on the banks of Allt a' Mhuilinn and climbs over Carn Beag Dearg (1010 metres above sea level), Carn Dearg Meadhonach (1179 metres above sea level) and Carn Mor Dearg (1279 metres above sea level) before crossing the Carn Mor Dearg Arête to get on to the Ben. I am sure that the views are worth it but a good head for heights is essential given the level of exposure.