If you've visited Paris before, it's likely that you've noticed a strange-looking building in central Paris. On rue de Rivoli between the Hôtel de Ville and Châtelet metro stops stands a tower. A tower that rises up alone and unattached to another building, surrounded by a small park. It's the type of monument you remember because it raises questions and elicits intrigue. Where is the rest of the building? Or is it supposed to be a tower standing on its own? What's it purpose?