It is a fulacht fia, the most common type of prehistoric monument found in Ireland, and yet the term remains unfamiliar to most people who pass near one. A fulacht fia is essentially the debris from an ancient cooking or hot-water site: stones were heated in a fire, then dropped into a water-filled trough to bring it to the boil, and the cracked, fire-shattered fragments were piled to the side over repeated use, gradually forming the characteristic mound. The one at Na Huláin Thiar measures fourteen metres east to west and eight metres north to south, rising to a height of 1.2 metres, which makes it a reasonably substantial example of the type.

What makes this particular mound quietly interesting is a detail recorded from local memory: around 1986, approximately 0.3 metres of burnt material was removed from the top of the mound. It is not an uncommon fate for these monuments, which tend to occupy useful agricultural ground and can be mistaken for natural features or inconvenient humps in a field. The removal means the original height would have been noticeably greater, and that some portion of the archaeological record, the uppermost layers of stone and organic debris that might have told something about the site's later phases of use, is now gone. The mound's location on the southern bank of a stream is entirely typical; proximity to a reliable water source was a practical necessity for however the site was being used, whether for cooking, textile processing, or bathing, all of which have been proposed by archaeologists studying fulachtaí fia more broadly.