The story of Aillwee Cave began millions of years ago when streams sinking underground on Aillwee Mountain started dissolving channels through the lines of weakness in the limestone. About one million years ago the ice age began and from then until fifteen thousand years ago Ireland's climate alternated between artic coldness and warmer periods, freezing and melting, freezing and melting over the centuries. This melting water roared and crashed it's way through an underground channel greatly enlarging the passage and bringing with it large quantities of sand and silts which are still present in the inner cave today. Aillwee is one of the most ancient caves in the Burren and perhaps in Ireland.