King David's DungeonCarved from sandstone, the dungeon (foreground) beneath England's Nottingham Castle (top)—scanned in 3-D via lasers—is superimposed on an image of the aboveground buildings. The pictures were created as part of the ongoing Nottingham Caves Survey, which began in March and intends to use the scans to help safeguard the man-made caves from "development, erosion, and ignorance," survey leader David Walker said. "We can compare future scans with current scans to see whether change has taken place." For centuries, Nottingham residents have taken advantage of the stable yet pliable sandstone beneath the city, carving everything from holding pens to World War II air raid shelters to beer cellars (some still in use). Sited on a sandstone outcrop, Nottingham Castle was rebuilt as a duke's mansion in the 1670s after the original structure had been destroyed during the English Civil War. The mansion's medieval caves, however, survived the conflict, including the dungeon, where King David II of Scotland was reportedly held prisoner in 1346. (Related pictures: "Return to the Crystal Caves.") —James Owen

Picture courtesy Nottingham Caves Survey