Caisteal nan Con (4)
The entrance was on this, the south-east side, the approach to it appearing (from lines in the turf) to pass immediately below the keep, from where it could be defended.  

It's hard to tell (from up here) whether the extension of the castle rock out into the bay, is geological or man-made (natural or unnatural).  I suspect it was probably a boat landing, built using the naturally occurring line of the volcanic dyke.

The perfect (turf covered) fan against the south-west face of the castle rock, presumably contains much of the masonry from the tower.
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