Beneath the floor of the broch is a fully preserved two-metre-deep rock-cut, subterranean structure, complete with a flight of stone stairs leading down into a main underground chamber.
This type of underground structure has been found at other brochs and Iron Age sites, and are usually termed “wells”.
They are actually not well understood, and their interpretation as a straightforward wells for drawing off quantities of water for ordinary everyday purposes, is in doubt.
The difficulty of access, including constricted entrances and steep staircases, has raised doubts about their functionality, and the volume of water found within them is seldom enough to have made much contribution to the needs of the broch community and their livestock.
The Cairns chamber is an amazing feature, comprising a series of seven stone steps descending two metres underground into a chamber that was carefully rock-cut, with a corbelled (bee-hive shaped) roof around two metres in height.
During the 2018 field season excavation of the waterlogged silts within the well yielded a remarkable series of organic items. Most notably a perfectly preserved wooden bowl was discovered, and several strands of human hair.
These and other finds from the structure will hopefully help us to better understand these enigmatic subterranean structures.