It measures roughly 4.4 metres by 3.3 metres and sinks only about 30 centimetres below the surrounding surface, unremarkable to anyone who did not know what lay beneath. When archaeologists excavated it in 2003, however, they found something considerably more interesting: a steep-sided pit nearly 60 centimetres deep, its waterlogged peaty fill preserving branches and twigs in the kind of anaerobic condition that rarely survives above ground, all of it resting on a compact layer of charcoal.

Radiocarbon dating of that charcoal returned a date of 585 plus or minus 20 years before present, a result that places the feature in a later medieval context, somewhere in the fourteenth or fifteenth century. What the pit was actually used for is not entirely settled. The excavators, publishing their findings through O'Brien in 2006, suggest it may have functioned either as a charcoal kiln or as a large roasting pit. A charcoal kiln was typically a carefully managed slow-burn structure, used to convert wood into charcoal for metalworking or other industrial purposes, while a roasting pit served a different function, sometimes used in ore processing. The presence of preserved organic material alongside the charcoal layer is what makes the site archaeologically valuable; such conditions allow researchers to examine the actual wood species used and the manner in which the material was laid down, details that are usually long gone by the time a site is found.