This is the nest of a Ringed Plover (Charadrius hiaticula) located in the surrounding rock of Strathy Point lighthouse. These delightful little plovers lay their eggs in a shingle scrape or like this one in a small depression in the grasses.
Beautifully camouflaged it was almost impossible to see from a few feet away and I was only made aware of it by the females antics of trying to distract me away.