Visited this site in Summer of 1997. Easy, short hike from SouthEast of the village of Kilmarie (cross stepping stones at the mouth of the burn, Abhain Cille Mhaire, and basically hug the coast on a fairly well-marked trail heading basically East). Site was fully accessible, in good shape and interesting – well worth the trip. The entrance was partly collapsed, but open.
Side note: the rock band Jethro Tull (on an album called ‘Stormwatch’) has a song called “Dun Ringill”. I do not know if the song references this site (I’ve not seen another of this name) or some imaginary place. Any Ian Anderson/Tull fans out there know?