I discovered a link on ABOUT: Alternative Religion (great site, tons of info plus pix) which was a newspaper article about a secret, and very weird, underground ossuary discovered beneath Paris. Dated 2004 though so maybe been discussed here before? It's worth checking out.
Unfortunately, the article doesn't mention a prize for anyone who solves the riddle of who created/used it...

http://altreligion.about.com/b/a/201432.htm

& the link page is: http://altreligion.about.com/gi/dynamic/of...99449%2C00.html

A little bit more hunting and I discovered the perpetrators; none other than The Perforating Mexicans!
http://www.guardian.co.uk/france/story/0,1...1302249,00.html

Long live free speech. And electricity!

Heehee, that's a good one Tas! I checked out the French media websites and found out this "Société de la Mexicain Perforation" is an underground artist movement of the "Cinema Noir" scene. A desk and a movie camera was found while the EDF (electric company) was quite upset about the "tapping" of their subterranean power lines. There are also other articles about this society helping the odd people get into the Palais de Versailles and the sports stadium for free through these underground passages. Sounds like a great way to tour Paris!

You probably saw this site already taz, hope your french is good!

http://www.showcaves.com/english/fr/misc/Catacombs.html

Those Perforating Mexicans rule! Wot a totally brilliant idea!

Mind you, I’m hardly surprised the French police over reacted at that, they appear to freak out at most situations....football matches for example...

I remember seeing the original story and thinking what a great thing to do. If only there were a similar group underneath London.....

I don't think it's be as much fun watching a movie in the sewer...

yup, sense of adventure!

Hardly the sweet smell of success though, eh

Olfactory ossuary makes access obfuscatory...

(Tas groans into her wee dram)

Obviously twas discovered whilst devotees were occupied in making obligatory observations, offering oblations, and oblivious to obnoxious odours!