Besides Robin Hood the city of Nottingham in England has another claim to fame. Beneath the city there are around 500 man made cave systems cut into the natural sandstone rock, many dating from medieval times. These have been used for everything from dungeons and air-raid shelters to beer cellars
The Nottingham Caves Survey team are attempting to map all these to millimetre precision using laser scanning equipment.
Their website has tonnes of background details with an interactive Google map of caves recorded so far, including links to descriptions, images and some amazing computer generated video fly-throughs like the one below.