This single wall, which looks like a tower when viewed from a distance, has obviously been the gable end of a larger building. Although its exact purpose is now unclear, it is commonly believed to have been a folly. However it is marked on 19th century OS maps as a beacon, and certainly its position near the summit of the Mull of Logan would have made it a conspicuous landmark when viewed from the sea.
Uploaded to Geograph by David Baird on 9 April 2013
Photo © David Baird, 9 April 2013. Licensed for reuse under this Creative Commons licence