Dun Cadha nan Ingrean lies on the west shore of Loch Slapin, just south of Kilmarie. For access, follow the road to Kilmarie Graveyard, and continue along the shore till the metalled surface runs out after about 1¼ kilometres. From here, an excellent track continues for another 250 metres till you encounter a wooden house on the left. Immediately after the house, head off very slightly east of south (i.e. left of the path) for 90 metres to the dun.
Like all the duns along this section of coastline, the way is beset by lush swathes of dense bracken, so if my experience is anything to go by you may have to hunt around for a while to find Cadha nan Ingrean.
The dun sits near a rocky point, above a steep descent towards the sea, as a tumbled mass of stones with very little discernable structure. There's lots of stone here though: piles and piles of it, so this must once have been an extremely impressive fortification.
Notwithstanding its current dilapidated state, this site is well worth the visit for the superb vistas it affords across Loch Slapin.