Most of us have probably dreamed, or somehow had to do, with a secret passage in their lifetime. As a child, one of my favourite ones was nothing more than the inside of a bedroom closet, where I just added a pillow to rest my back comfortably.
Used by rulers and wealthy citizens since the dawn of time, a secret passage is now found practically everywhere, from ancient castles to period buildings, but also in completely normal apartments. If you have a fairly spacious house, the simplest method seems to be the bookcase. Otherwise, when the space is a little tight, the wardrobe can become your special refuge.