The City of Caves attraction is built around one of the oldest surviving sets. Pottery finds date some of these chambers to between 1270 and 1300, which makes them roughly contemporary with the rebuilding of Lincoln Cathedral. The Pillar Cave was originally cut around 1250, collapsed in a rockfall by 1400, and was cleared and reopened in 1500 to serve a new purpose: the only known underground tannery in Britain. Two caves opening out to daylight at the cliff face were fitted with circular pits to hold barrels of liquor, and rectangular clay-lined vats for soaking the skins. The vats are small. They were almost certainly used for sheep and goat hides rather than cattle. There was an opening to the River Leen, where the tanners washed the raw skins in what was, inconveniently, also the town's drinking water.

Above the caves once ran Drury Hill, a narrow medieval street that had been wealthy in its day and had become, by the nineteenth century, one of the worst slums in Britain. The basement walls preserved underground are all that remains of those buildings. Families lived in the single rooms that had been hollowed into the rock — slept, ate, and conducted whatever working life they could manage in a few cubic feet of cold sandstone. Overcrowding kept the rents high and made the rooms efficient incubators for cholera, tuberculosis, and smallpox. The St Mary's Nottingham Inclosure Act of 1845 finally banned the renting of cellars and caves as homes for the poor, but a basement is only as good as the alternative on offer, and many families did not have one until well into the new century.

By February 1941, Nottingham City Council had located eighty-six public air-raid shelters in the sandstone beneath the city. Some were natural extensions of the medieval caves; others were freshly dug to connect them. The bombing came in waves but never on the scale of Coventry or London. The exception was the night of 8 May 1941, when a German raid concentrated on Nottingham and people sheltered in numbers in the caves under Drury Hill. The City of Caves tour recreates that night with sound and light. The same caves doubled as a sand source for the city's sandbags, with new shafts cut to deliver the material to street level. Within a generation, the war was over and the caves had returned to silence.

The reason any of this is visible today is a planning fight that nearly went the other way. Construction of the Broadmarsh Shopping Centre began in the late 1960s, and the project initially proposed to fill the caves with concrete — partly because the open chambers were a security and safety hazard, partly because nobody was sure what to do with them. A public outcry followed. A detailed survey by Nottingham City Council and the Nottingham Historical Arts Society led to the caves being scheduled as an ancient monument. Volunteers from the Air Training Corps and Rushcliffe School cleared them by hand. The Friends of Nottingham Museum opened them to public tours in 1978, and the formal City of Caves visitor attraction — now part of the National Justice Museum, run by the Egalitarian Trust — opened in 2004. The shopping centre above closed and is being rebuilt; you currently enter the caves from Garner's Hill.

Most cities sit on the ground they occupy. Nottingham has been hollowing out underneath itself for so long that the rock beneath the streets is shot through with rooms — pub cellars and ice houses, malt kilns and storage chambers, tanneries and shelters and slums. Tig Guocobauc, Asser called it. The Welsh syllables are a thousand years stale but the place they describe is still down there, doors and arches cut by hand into a rock soft enough to give and stubborn enough to remember.