Indenting your wood with dado cuts should make it easier ... drill holes in the top and bottom of the secret bookcase door ...

AMAZART FURNITURE Wood Corner Book Shelf with Glass Door, Wooden Bookshelf for Home Library, Crockery Cabinet, Kitchen Display Cabinet, Book Rack, Book Stand, Wooden BookCases, Shelves, Honey ...

Step forward: a BILLY bookcase with glass doors and a black trim ... All you need to do is get a wooden panel of the right height and width, to stick between numerous BILLYs across a whole ...