Over on hideadoor.com, they have a number of idea on ways you can have a secret door in your own home. Find out more here.
Also, on iliketomakestuff.com, they show you how to make your own secret door bookcase here.
Finally, from the peterjb62 YouTube channel, a clip from Young Frankenstein (1974) showing the late Gene Wilder and the great Teri Garr searching for a secret door with varying degrees of success. Enjoy!