For over a year in the mid-2000s, members of the group Untergunther broke into the French Pantheon and repaired a clock which had been broken for 40 years. They were later taken to court for their efforts and eventually let off with a warning. In 2018, one of the members, clock restorer Jean-Baptiste Viot, was hired to repair it after it was further neglected. – WTF Fun Facts
Source: Secret French illegal clock restorer gets the job (connexionfrance.com)