The rath at Caherglassaun sits on the summit of this modest rise, its circular form still clearly legible in the landscape despite centuries of agricultural use around it.

A rath is an early medieval Irish ringfort, typically a circular enclosure defined by one or more earthen banks and a surrounding ditch, used as a defended farmstead or residence. This example measures thirty-eight metres in diameter, with a bank and an external fosse, the fosse being the ditch dug to reinforce the bank's defensive profile. What sets it apart slightly from more eroded examples of its type is the condition of some of its internal detail. Traces of an inner stone revetment, a facing of stone used to stabilise and strengthen the bank from within, are still intermittently visible, suggesting the original construction involved more than simple earth-piling. The southern side retains a stone-lined causewayed entrance gap of roughly two and a half metres wide, where a raised pathway would once have crossed the fosse to allow entry. The fact that the entrance survives in this form, rather than as a simple break in the bank, is a reminder that these enclosures were carefully engineered rather than casually thrown up.