What is a souterrain?

Answer 1

Many raths had underground passages known as souterrains. These passages were lined with stones and may have acted as a type of Iron Age fridge to keep meat and other foods cold. Valuables could also be be stored here and families may have taken refuge in souterrains during raids. Some have been reported to act as a tunnel connecting to another area for escape or safe travel. There's a rath near my house with a souterrain linking two places but was filled up with stones as it was condemned unsafe.