Panthéon officials and guards were unaware of the activity until the restoration was complete and the group asked an administrator to try winding up the clock. (The cultural ministry overseeing the monument later fired the administrator.)
According to The Guardian, the Untergunther gets into a lot of fun stuff:
Since the 1990s they have restored crypts, staged readings and plays in monuments at night, and organised rock concerts in quarries. The network was unknown to the authorities until 2004, when the police discovered an underground cinema, complete with bar and restaurant, under the Seine.
Just one question: How do I join? Click here to read the whole story.