Defying explanation

A guided archaeology tour across the mountain led to several familiar sites and some less so. 
What are we to make of this rectangular depression with vestiges of a wall-and-ditch enclosure along with a mound in the middle crowned by a pile of loose stones? Could it have been a burial site, a hut circle, a summer dwelling or an animal pen?  Without excavation it remains a mystery and even if investigated it may not yield its secret.

Nevertheless, a fine afternoon for a hilltop ramble.