Most people who pass it take it for an ordinary field boundary. It is, in fact, the most complete surviving high medieval deer park in Ireland, and its wall has been standing, more or less intact, since the thirteenth century. Of 193 locations surveyed along its course, only 36 had lost all trace of the original stonework. In places the limestone courses still reach 2.6 metres, built in double-face construction with a mortared rubble core, the same technique that raised it when Loughrea itself was a new town.

The park was established by the de Burghs, the Anglo-Norman family who founded Loughrea in 1236, and radiocarbon dating of charcoal from a mortar sample places its construction between 1251 and 1297. Documentary sources confirm the park's existence by 1333. The wall was engineered with a particular logic: the ground inside was deliberately kept lower than the ground outside, so that deer could drop in from the surrounding landscape without much difficulty but would face an uphill jump if they tried to escape. Two gateways controlled entry, one to the north-west and one to the north-east. The north-eastern example, at just over three metres wide, was built to admit carts, and geophysical survey of the disturbed ground outside it hints at a cobbled yard and track. A large flat slab at the junction of two relict trackways near the north-western entrance is still called 'The Resting Stone' locally, a name that recalls the working life of those old routes. Stranger still is a small squared aperture, roughly 20 centimetres in each direction, set into the original wall near what may have been an eastern entrance. Sitting about 80 centimetres off the ground, it appears to have been a deliberate feature, possibly used to pass small items in and out of the enclosure without opening a gate. The park's boundary is exactly coterminous with the townland of Earlspark, suggesting the two boundaries have been understood as identical for centuries.

The enclosed area also contains a remarkable density of earlier monuments that predate the deer park entirely: two hillforts, two enclosures, a ringfort, a field system, a souterrain (an underground stone-lined passage, typically associated with early medieval settlement), a standing stone, and a children's burial ground. The de Burghs built their hunting ground around a landscape already layered with centuries of occupation, which gives the whole place an unusually compressed sense of time.