 In Switzerland, there is an unusually large number of bunkers because of a law requiring protective shelters to be constructed for all new buildings since 1963, as well as a number of bunkers built as part of its National Redoubt military defense plan.Some of Switzerland's bunkers have since become tourist attractions housing hotels and museums such as Sasso San Gottardo Museum.The Soviet Union maintained huge bunkers (one of the secondary uses of the very deeply dug Moscow Metro and Kyiv metro systems was as nuclear shelters).