This sheer-sided rectangular notch in the coastline on the northwestern side of the Butt of Lewis looks almost to have been quarried - but I think the quarrying is entirely natural and caused by the remorseless action of the pounding North Atlantic.
Uploaded to Geograph by Rob Farrow on 26 August 2011
Photo © Rob Farrow, 26 August 2011. Licensed for reuse under this Creative Commons licence