Mapping the Underworld: Digital 3D Cave Exploration

Just under the surface of Nottingham, England, there’s hidden world ripe for exploration, from a 14th century dungeon that once reputedly held a king prisoner to a 19th century butchery. Not just anyone can get to most of these 450+ sandstone caves, many of which are located under Nottingham Castle, and they’ve never even been accurately mapped – until cutting-edge laser technology made these incredible 3D scans possible. The Nottingham Caves Survey has already recorded the shape and surface details of 35 caves, layering them with above-ground photos to give us an unprecedented and surprisingly artistic view.

As part of the Caves of Nottingham Regeneration Project, the Nottingham Caves Survey is taking 3D laser scanners into the depths beneath the city to photograph the caves, survey them with the scanner and note their condition. Many of these caves have major historical significance for Nottingham and for England – the earliest written record of caves beneath what was then a Saxon settlement dates to the year 868. The project aims to protect the caves, in the hopes that they won’t simply be forgotten and allowed to deteriorate.

King David’s Dungeon

The soft, carvable sandstone under Nottingham provided an ideal medium for creating these artificial labyrinths. Holes were dug with hand tools to create underground homes as well as space for activities like tanning, pottery production and even beer malting. Some were used as storage areas, hidden passageways and supply tunnels.    The medieval caves under Nottingham Castle, which was rebuilt in the 1670s after the original structure was destroyed in the English Civil War, include a dungeon in which King David II of Scotland was reportedly held prisoner in 1346.

Mortimer’s Hole at Nottingham Castle

Another tunnel under the castle has an even more fascinating story. Mortimer’s Hole is named after Roger Mortimer, rebel and lover of the power-hungry Queen Isabella. The duo overthrew Isabella’s husband, King Edward II, and were living at Nottingham Castle when Isabella’s teenage son, King Edward III, invaded to take his rightful place. The King’s troops used the cave to sneak into the castle and capture Mortimer, who was subsequently hanged.

It’s an intriguing legend, and the ‘official’ Mortimer’s Hole has become a tourist attraction at the castle, complete with guided tours. But the survey team have discovered another tunnel that they believe is far more likely to be the actual tunnel used in the invasion. ‘The Real Mortimer’s Hole‘ matches historical records of the capture.

Castle Gate Medieval Malt Kiln & Breweries

Some of the sandstone caves were used for malting and other aspects of beer production, which is a major aspect of Nottingham history. Each complex of caves included a germination room where grain was prepared, the kiln where it was roasted, and a deep well to reach water. The benefit of brewing in caves is the constant year-round temperature.

Drinking Den Under Nobleman’s House

The beer-related activity that went on deep beneath the surface of Nottingham wasn’t limited only to production. This carved underground space beneath Willoughby House, an 18th-century aristocratic manor, was likely a drinking den. It includes built-in banquettes and a wine cellar.

Nottingham Castle Brewhouse Yard

Beer was once stored in the caves at ‘Brewhouse Yard’, a system of caves found adjacent to a group of five 17th century cottages. The cottages are all that remain of a once-thriving community, and now house The Museum of Nottingham Life.

Air Raid Shelters at the Guildhall Caves

The brick-lined passes and cells beneath Nottingham Guildhall, a 19th century building housing the magistrate’s court, central police station and fire station, are some of the most modified underground passages found in Nottingham. They were extensively re-worked during World War II for use as emergency headquarters and air raid shelters.

Peel Street Cave System

The Peel Street mass of subterranean tunnels definitely seems to qualify as a maze. It may seem strangely chaotic for a man-made set of passageways, but that’s because its purpose was different from all of the others in Nottingham: it was actually a sand mine. It’s thought that the mine was in use between 1780 and 1810, but the caves were forgotten until 1892, when they became a tourist attraction called “Robin Hood’s Mammoth Cave”.

Scanners at Work

To capture these strange digital imprints of vast underground spaces, the Nottingham Caves Survey crew hauls equipment below the surface on bike trailers. The scanners send beams of laser light deep into the caves and measure the amount of time it takes for the light to return. The scanners can capture an incredible 500,000 survey points per second, creating a ‘point cloud’ that results in a 3D image.

“The experience of visiting these domestic caves is far removed from the clean regularity of modern urban living and offers a tangible link to medieval Nottingham,” explains the project team. “This is particularly significant in a city with such a strong past personality but so few medieval structures still standing above ground.”