The doorway on its north side is just fifty-five centimetres high and fifty centimetres wide, a deliberate squeeze that was very much part of how the building worked. This is a sweathouse, a type of native Irish sauna found scattered across the northern counties, and the one at Port in County Cavan is a fine, compact example of the form.

Built in the dry-stone beehive tradition, meaning corbelled courses of unmortered stone that tighten inward and upward until closed off at the top, the structure stands 1.9 metres high and measures just 1.3 metres across internally. Two flat slabs form the roof. The method of use was straightforward: a fire would be lit inside, the space allowed to heat thoroughly, the embers cleared out, and then a person, or perhaps a few people, would crawl in through the low entrance and sweat in the retained warmth. Richardson, writing in 1939, noted a chimney on the south side, which would have served the heating phase before the structure was prepared for occupation. Sweathouses of this kind were folk therapeutic structures, used to treat ailments ranging from rheumatism to fevers, and they appear to have remained in local use well into the nineteenth century before gradually falling out of practice.

The interior diameter of 1.3 metres gives a sense of just how intimate, and how physically demanding, the experience must have been. The low entrance also served a practical function, helping to retain the heat once the door was sealed during a session. What survives at Port is a quietly self-contained piece of vernacular medical architecture, modest in scale and easy to overlook, but carrying a very specific and once widely understood purpose.