The Musée Bricard, or Musée de la Serrure, was once one of Paris’s tiny hidden gems. The curious collection features locks and keys dating form Roman times up to the present day, including one lock that attacks anyone who uses the wrong key, and a metal masterpiece created by a locksmith who was himself kept behind locked doors during the four years it took him to complete it. The museum is currently closed to the public, though hopefully will be reopening soon.