Secret Rooms and Passages

WebUrbanist has a great story today about secret rooms and passages. Some of them are well-known, and most are kind of gory (like the secret murder room constructed by H. H. Holmes, which you can read all about in The Devil in the White City by Erik Larson). The coolest one, I think, is the secret bookcase door at the Mont Sainte-Odile convent library (see photo above). I definitely need one of these for my dream library!