A lead castle, also called a lead cave or a lead housing, is a structure composed of bricks made of lead. Lead castles are a type of lead shielding and are used to enclose small radioactive sources and/or radiation detectors. They are used during nuclear research and testing. The castle may enclose the radioactive source to shield people from radiation or it may be used to shield sensitive detectors from ambient gamma radiation. If the experiment is to be observed, a viewing window of lead glass may be used. A typical lead brick weighs about ten kilograms. Lead castles can be made of hundreds of bricks and weigh thousands of kilograms, so the floor must be able to withstand a heavy load. It is best to set one up on the ground floor[1] or basement of a building built on a concrete slab. If the castle is not put directly on the floor, it will require a very strong structure to safely support it.