Big souterrain from fort is escape passage and cool food storage
Unlike the muddy Souterrains that one had to crawl through around Knowth, and the ones one feared might collapse on you in the Beehive houses and prominatory forts of the Dingle Peninsula, the Souterrain at the Ring Fort of Craggaunowen is tall and dry and easy to navagate (although quite dark in the unlighted chambers). One can tell that this souterrain was meant to be used regularly. It starts in the fort but has an outside exit that could be used for escape as well.
Souterrain of Craggaunowen Ring Fort, a true reproduction of a farmer's house, dating from the 4th or 5th century. Ring forts, of which there are about 40,000 examples throughout Ireland, were the standard type of farmstead during the early Christian Period (5th -12th centuries AD).
The Souterrain - An underground passage was designed primarily as food storage areas, ventilated, but draft free, souterrains maintain a constant temperature of around 4 degrees no matter how hot it gets on the surface. They could also be used as places of refuge during attacks on the Ring fort, many souterrains have secondary or tertiary chambers which are difficult to enter, thereby affording their occupants a measure of security.