The Cailleach Bheur was a blue hag, said to frequent parts of the Scottish Highlands. Associated with winter, she was reborn on every All Hallows Eve and returned to bring the winter and the winter snows. She carried a magical staff, which froze the ground with every tap. She was also guardian to animals throughout the winter, and returned to the earth by turning to stone on Beltane Eve. In other traditions she changes into a young maiden, suggesting the changing phases of an earth goddess. Her sacred trees were the holly and the gorse bush, under which she traditionally threw her staff before turning to stone.

She may be related to other similar figures found throughout Britain, (see Black Annis) possibly worshiped by the ancient Britons. The Irish version, the Cailleach Beare is similar although not as specifically winter orientated, and may according to Donald Mackenzie, 'Scottish Folklore and Folklife' be younger than the Highland version. Archetypal she seems to incorporate the crone aspect of the earth goddess or the goddess of winter.

There are several stories told about her. One story attaches her to a specific place; she was charge of a well on the summit of Ben Crauchan in Argyll. Every sunset she had to cap the flowing water with a large flat stone and then release it at sunrise.

One night, weary from driving her goats across the mountains, she fell asleep by the side of the well. Unhindered the water gushed forth, breaking through at the Pass of Brander creating Loch Awe, and drowning local people and cattle in its wake. She was so horrified by her mistake that she turned to stone. The overflowing well is a common folklore motif used to explain many lakes and lochs.

There are many such crones or hags in British folklore, and they may all have a similar root source. Her association with stone is unusual, and she may have been identified with certain standing stones, perhaps, and this is pure speculation, ones with winter astronomical alignments.