It might not be obvious from the size of the image, but the man right on the cliff edge is taking a ‘selfie’ with his camera phone (I wonder if I’m in the background). The wall behind him is part of the fortifications at Dun Aengus (Dún Aonghasa) on Inis Mór, the largest on the Aran Islands off the Galway coast. You can see a bigger version of the picture here. A wide-angle view taken at the same time, of the same scene, can be seen here.