As far as i could see these 2 crevices were interlinked on the cliff face. There seemed to be 2 puffins going in and out of here. The Bempton cliffs are steep and there was plenty of puffin activity at sea level according to a guy with an adjusted telescope. He let me have a look and sure enough the little birds were quite plentiful there, but I couldn't recoginise them without the telescope. These puffin 'burrows' were about a third of the way down the cliffs, and just withing the zoom distance of my lens.

The cliffs are chalky and seem to be held together by guano.