Here's a story I found on both, the BBC and Spiegel Online.

A female British tourist managed to get herself trapped in a French town hall, after the tried to check in at the impressive looking "Hôtel de Ville". The traveller, who is said to be in her thirties, had not booked accommodation when she arrived in the Alsace town of Dannemarie. Not realising, that the hôtel de ville is the town hall, she'd entered the building late on Friday and gone to the toilet before she wanted to go to reception and get a room.

However, while she was in the restrooms, a late meeting finished and the town's politicians locked the door behind themselves, not hearing the water flushing. When she came back out, she found herself locked in. After spending the night on chairs in the lobby, she wrote a note that she posted on one of the building's doors. It read "'Je suis fermer ici. Est ce possible moi la porte ouvrir?" which translates to "I am to close here. Is it possible me the door to open?". The note was spotted on Saturday morning and Dannemarie's mayor Paul Mumbach let her out.

Dannemarie itself has no hotels, although it is close to the Swiss and German borders. The mayor now thinks about putting up multilingual signs, for English- and German-speaking tourists.