On the road out of Fort William that goes to the two Stiell Falls you have Ben Nevis on your left and Nevis Forest on your right. Go along this road as far as the peat track that is part of the Cow Hill Circuit in the forest. At the top where it meets the West Highland Way several directions are signposted including that for 2.8km (ha, ha) to this vitrified fort. A long steady walk along the forest road.
Eventually you reach the point where the signpost points to the Dun Deardail track off the West Highland Way. You go over the most incredible turnstile, of such a size you could literally take a pram over it - except the track is strictly for the feet. It is basically a gravel path consolidated by black bags of something spongy underneath, so that you have the strange (and at times disconcerting) feeling of walking on a deep forest floor.
Just before the fort is a big hill called An Dun despite being nothing of the sort, purely natural. At one marshy spot there is a duckboard walk. I cannot recommend this site to anyone that is not either very sure of foot or else foolhardy - you imagine beforehand someone will have made a level route straight into the interior of Dun Deardail but instead find yourself clambering up the steep sides on a not-quite-straight stony path. The narrow path is composed of different materials, the right hand section (below the level of the left by several inches) is all fragmented planes of presumably bedrock whilst the left is small boulders and rocks, the right all grey but the left of differing hues not all owing to vitrification. I think in far drier weather climbing over the turf would have been my choice instead. Once you do reach the top its mostly depression, with a narrow outer circuit at the edge of the sharp drop about the site.
There are what appear to be reasonably sized structures around the edges of the interior but my view was rather damp and this really is the wrong season for a major recce unless you can get around nettles and such.
Dun Deardail is one in a line of vitrified forts that stretches from Craig Phadraig outside Inverness all the way down to the West Coast. Most of its names refer to a fancied connection with Princess Deirdre (see miscellaneous) but it is also known as Dun Dearg Suil 'Hill of the Red Eye'. This has been read as a reference to usage as a beacon hill when surely one could as well read in a folk-memory of its vitrification or an astute inference by analogy that this had happened.
The crag of Dun Deardail is 700' high and the fort is 925' above sea level. So it might be easier, though taking longer, to follow the Way through Nevis Forest ! The Way has the nearest turn-off down to the main road at Dun Dige.
"Fort of the Red Eye". This ruinous vitrified fort (RCAHMS NMRS record no.NN17SW 6) would seem to hold a similar position relative to Fort William as Dun Phadraig (also vitrified) does to Inverness. An enclosure wall runs about a natural knoll on the E & W & N, and a 4m D depression in the northern area of this is a well/cistern beside a marshy area.