The UX (for Urban eXperiment) is an underground organization that improves hidden corners of Paris. Their works have included building a cinema, complete with bar and restaurant, underneath the Trocadéro, restoring medieval crypts, and staging plays and readings in monuments after dark. The group's membership is largely secret, but its spokespeople include Lazar Kunstmann.
The Parisian authorities oppose the group's actions, starting a police unit to track them through the sewers and catacombs of Paris, and attempting to apprehend and charge them.
The organization is divided into teams: an all-female team specializing in infiltration, a team running an internal messaging system and coded radio network, a team providing a database, a team organizing underground shows, a team doing photography, a team (Untergunther) doing restoration. One project, La Mexicaine de Perforation (LMDP), built an underground cinema, Les Arènes de Chaillot, next to the Cinémathèque Française.
Untergunther's membership includes architects and historians. The team has renovated a century-old abandoned government bunker and a 12th-century crypt. In October 2007, they received attention for a project, assisted by professional clockmaker Jean-Baptiste Viot, to clandestinely restore the famous clock in the Panthéon. Never caught, upon completion they announced their work at a meeting with the administrator of the Panthéon, who called the police. Charges were brought against the four but, at trial, after twenty minutes deliberation, the judge ruled in favor of Untergunther.