Mine Howe is an unusual structure. From outside it looks like an ordinary low mound on the gentle farmland of Tankerness, five miles southeast of Kirkwall. But cut into the top of the mound is a small entrance, and beneath that entrance is a flight of stone steps that descend at a sharp angle into the body of the hill. After a few metres the steps reach a half-landing where they turn back on themselves, hairpin-style, and continue down. Two more passages open off the landing, one above the other, like side chapels in a church. At the bottom of the second flight is a chamber roughly 1.3 metres across and over four metres high, a vertical drystone shaft with a corbelled roof. The bottom step into this chamber is itself nearly a metre tall, giving the whole space the look of a cistern dropped into bedrock. The drystone walling throughout is the work of Iron Age masons who knew exactly what they were doing.

The word howe comes from the Old Norse haugr, meaning a barrow or burial mound. The Norse settlers who arrived in Orkney in the eighth and ninth centuries AD used the term for the hundreds of low prehistoric mounds they found scattered across their new homeland, most of them already a thousand years older than the Vikings themselves. Mine Howe was one of these. Built roughly two thousand years ago during the Iron Age, it bears some resemblance to the well inside the Iron Age Broch of Gurness elsewhere in Orkney, suggesting it may have served a similar function. Brochs were defensive towers; their wells gave the besieged inhabitants access to water and possibly to ritual practice. Mine Howe has no broch above it, however, and no firm conclusions have been reached about whether it stood alone or was part of a larger lost settlement.

Mine Howe was first explored in 1946 by archaeologists who concluded, wrongly, that it was an Iron Age broch. The classification did not fit; brochs are above-ground stone towers, and Mine Howe is the opposite. The excavation was small, the findings inconclusive, and afterwards the entrance was covered over and the site was effectively forgotten. For fifty years it sat untouched beneath the farmland, the steps still descending into darkness, the chamber still holding its silence. Douglas Paterson, the farmer who owned the land at the end of the twentieth century, knew the family stories about a hole somewhere on the rise and started looking. When he found it in 1999 he cleared out the silt, built a small wooden shelter over the opening, and constructed handrails on the steps so visitors could descend safely. He had become the unofficial custodian of a site that nobody fully understood.

In June 2000 the British archaeological television programme Time Team arrived at Mine Howe with cameras, presenter Tony Robinson, and a three-day deadline. They dug trenches around the mound, exposed sections of an external ditch that had once surrounded the structure, and traced what appears to be an earthen path leading visitors to the entrance. To work out how the chamber had been built, the team constructed a small replica nearby and tried to drystone-wall the corbelled roof themselves. The replica suggested that Iron Age masons would have needed scaffolding and a clear understanding of the loading pattern at each course; this was not casual construction. The Time Team excavation also turned up evidence of metalworking on the surrounding mound, raising the possibility that Mine Howe was associated with an Iron Age industrial or ritual workshop. None of this resolved the central question: what was the underground chamber for?

The space at the bottom of the steps is too narrow to hold many people, too high to be a storage cellar, and too elaborate to be merely a well. Theories include a ritual immersion chamber for water cult practice, a votive site where offerings were lowered into the earth, a sound chamber for ceremonies (the acoustics are striking), and a sanctuary connected to the metalworking on the surface. None has been proven. Mine Howe sits on private farmland but is occasionally open to visitors during the summer; descending is not for the claustrophobic. The chamber at the bottom is dark, narrow, cold, and absolutely silent, the noise of the wind and the gulls and the modern world stopped completely once you are below the lip of the entrance. Whatever the Iron Age builders intended this space to feel like, it almost certainly felt like this.