A cashel is a type of early medieval enclosure, typically a roughly circular stone-walled compound that once protected a farmstead or small settlement. Within this particular example at Derreen, positioned slightly west of centre, lies an even older and quieter presence: the foundation of a single circular hut.

The structure is modest in its dimensions, with an external diameter of 4.5 metres and a defining bank of earth and stone that ranges between 0.6 and 0.7 metres in width. What makes it more than just a ring of rubble is a gap on the northern side, approximately 1.8 metres wide, which may represent the original entrance. The oval cashel that contains it has its own separate record, but the hut foundation within is a distinct feature, a structure inside a structure, suggesting that this small enclosure was once a functioning domestic space rather than simply a symbolic or defensive boundary. Whether the hut predates the cashel, or was built as part of the same phase of occupation, is not something the physical remains alone can answer.