An enclosure is located on Pengwern Common (Lunnon Moor), on the immediate north side of the B4271 road which traverses the common. Oval on plan, it measures some 50m (NE-SW) by about 30m within a broad grassy bank broken by a narrow gap on the north.
The enclosure appears to lie on a low spur which projects from ground falling away moderately steeply to the north, on the south side of a stream valley which drains this side of the common. The bank is 10m-11m wide and is most pronounced on the north where it is 0.75m high externally, 0.5m internally. The bank stands out as a band of dry, bracken-grown ground surrounding a gently-sloping, poorly-drained, gorse-grown but otherwise featureless interior. The bank diminishes in height and width as it fades into rising ground to the south, close to the road. A minor stream trickles through the narrow break in the bank. Probing of the bank suggests it is of earth construction but low down at the 'entrance' probing indicates a stony core. Although it has the appearance of a built bank there is no obvious ditch associated with it. The enclosure is visible on aerial photographs. Similarly dry areas can be seen on the Common, to the north and west, but none has the same configuration and appearance of enclosure. For the moment, its date and function are unknown.
It is possible that the site is a natural feature. It lies close to the southern limit of the last ice sheet, which crossed central Gower, and where periglacial features might form. The structure could be a `pingo? created when water trapped beneath superficial deposits expands on freezing to form a mound which eventually collapses on thawing leaving a circular/oval `rampart? surrounding a pond. If so, the boggy interior might conceal a depth of peat containing a valuable palaeo-environmental record for the post-glacial period in this relatively low-lying locality.
