http://en.wikipedia.org/wiki/Secret_passage#1900_.E2.80.93_present
http://imgur.com/gallery/zChSf, http://en.wikipedia.org/wiki/Panic_room
http://hiddenpassageway.com
http://mentalfloss.com/article/51949/13-houses-secret-passageways
http://www.buzzfeed.com/awesomer/31-beautiful-hidden-rooms-and-secret-passages
https://www.google.ca/search?q=secret+passages&safe=off&espv=210&es_sm=93&tbm=isch&tbo=u&source=univ&sa=X&ei=hxCIUtO3Ooj12QXLjYHYBg&ved=0CDMQsAQ&biw=1422&bih=775&dpr=0.9