Aillwee Cave was first discovered in 1940 by local farmer Jack McGann who followed his dog into the cave. It wasn’t until 1973 that he told cavers about it and by 1977 the cave had been fully explored and mapped. Formed by water flowing through cracks in the limestone hill, it is one of the oldest caves in the Burren and contains bear bones, stalactites, stalagmites and an underground waterfall. The limestone terraces on the hill behind the cave contain evidence of fossil soils that are over 300 million years old.
Aillwee Cave has a long complex history and radioisotope data suggest the cave is more than 1 million years old and was already formed before the last major ice advance. It was formed by rainwater dissolving the limestone as it flowed from the surface through vertical fissures called ‘grikes’ in the limestone over long periods of time. Water continues to flow in parts of the cave although the main passage is now inactive and dry.
The bones of bears found in Aillwee Cave and the shallow pits discovered in the passage suggest bears may have used the cave for hibernation. Aillwee Cave may have been one of the last refuges of the Irish Brown Bear. DNA studies have shown that the Irish Brown Bears bred with polar bears which travelled along the margins of the retreating ice sheets at the end of the last ice age.
The base of the rocky terraces on Aillwee Hill mark the position of thin clay or shale layers in the limestone. These shale layers are thought to mark periods of exposure when sea-levels were lowered due to an ice age 330 million years ago. As sea-levels dropped the seafloor was exposed to weathering and soil formation. The subsequent sea-level rise covered these layers with limestone again. These clay layers are impermeable barriers to water and springs often emerge where they occur.