When I was in Paris I visited the famed flea market, the Marché aux Puces de St-Ouen. I found a tiny store that specialized in antique hardware, and a box labeled old hotel keys. 1€ each. I bought one. Then we stopped at the café it occurred to me that these might be a good souvenir for some of my friends at home, so I found my way back through the maze to the little shop and purchased several more. I should have bought the whole box.