It is easy to walk past without registering what you are looking at, which is partly what makes it worth understanding. This is a rath, the Irish term for a ringfort, the kind of enclosed farmstead that once dotted the countryside in extraordinary numbers during the early medieval period, roughly between the fifth and twelfth centuries. Tens of thousands once existed across Ireland; many have been ploughed away or built over, while others like this one persist, worn down but still legible in the landscape.

The site at Coolrus was recorded by Denis Power and uploaded to the national record in August 2011. It takes a roughly circular form, measuring approximately 25.5 metres on its north to south axis, and is defined by an earthen bank, the kind of boundary that would originally have enclosed a farmstead, perhaps sheltering a family, their livestock, and their outbuildings. The bank survives to an internal height of around 0.75 metres and an external height of 1.3 metres, meaning it reads more prominently from outside than from within. A shallow fosse, the ditch dug when the bank was raised, runs from the north-west around to the east. The difference in height between the inner and outer faces is a function of how these earthworks were constructed; earth dug from the fosse was piled inward to form the rampart, so the external face, rising from the base of the ditch, always appears taller.

Accessing the site requires some patience. Much of the interior is obscured by dense vegetation, fallen timber, and dumps of earth, so reading the form of the monument on the ground takes a little effort and a willingness to move around the perimeter rather than push straight through. The surrounding pasture is flat, which at least makes the line of the bank and fosse relatively easy to trace once your eye adjusts. Late autumn or winter, when leaf cover has dropped, generally gives the clearest sense of the earthwork's outline. As with many such sites on private farmland, approaching with care and awareness of land ownership is sensible.