They look like stone igloos and might be described as Irish-style saunas.
Sweathouses were popular in the 1700s but their use died out towards the end of the 1800s and into the 20th century with the advancement of rural dispensaries.
There are more sweathouses in Co Leitrim than anywhere else in Ireland.
Now the county council there has launched a community archaeology project to collect and catalogue all existing sites as well as any oral histories about them.
The small stone structures were built into the slope of a hillside, or covered with sods of earth in isolated areas, often near a stream or other water source.
Archaeologist Aidan Harte, who is leading the Leitrim sweathouse project, said they would be packed with turf or wood which was let burn until all the stones in the structure heated up.
Then the ashes were raked out and reeds spread on the floor before the person using it would remove their clothes and crawl inside to "sweat out" whatever ailed them.
The sweating cure was commonly used for fevers, rheumatism, arthritis and gout among other conditions.
Some people ascribe a Scandinavian link to the practice but Aidan Harte said that, in truth, the origins of Irish sweathouses are unknown.
Leitrim County Council Heritage Officer, Sarah Malone, said the project aims to connect with Leitrim people young and old.
It is seeking volunteers to research archives and record oral histories so that they can gather as much information as possible and celebrate "this unique part of our culture".
The project is being supported by the Heritage Council and has already seen a number of previously unrecorded sweathouses in Leitrim identified by local people.