The enclosure at Coolquill is a deer park, roughly rectangular and covering a substantial area of ground, its interior now given over to a coniferous plantation rather than the managed woodland and grazing that would once have sustained a population of deer for aristocratic hunting.

Deer parks were a commonplace of Norman and later medieval lordship in Ireland, attached to castles as a marker of status and a practical source of game. At Coolquill, the associated castle sits at the western angle of the enclosure, the two features forming a single designed complex. The wall itself, 0.6 metres thick and still standing to about 1.2 metres in height in places, would originally have been built high enough to prevent deer from escaping, a detail that occasionally shows up in surviving examples elsewhere in the country. What makes Coolquill particularly interesting is the presence of a possible motte near the centre of the deer park. A motte is a raised earthen mound, the defining element of an early Norman fortification, and finding one apparently sitting inside the later deer park raises the question of which came first and how the two features relate to one another across what may have been several centuries of use and reuse of the same ground.