With this mysterious game board inside (bonus points if you know what this is - French citizens are excluded as I am sure they know!)
And a very carefully crafted collage on the reverse.
No return address, but I do have a list of French mail artists who send me things, so I did a little detective work based on the writing and the 'R'L' of the rubber stamp.
Turns out Raphael'L at IUOMA sent out an interesting series of these recently. The mystery was unintended, I think she just forgot to add a return address, or anything inside to indicate who it was from.