This custom bookshelf door was made by Dowd Temple Designs. It doesn’t pivot or slide to the side like many secret doors, but pushes straight back on casters to reveal a large walk-in closet space.
These IKEA bookcases are connected together, then mounted on casters and large gate hinges to create a secret door. A “how-to” article is located on IKEA Hackers.The extra wide door pivots open to reveal a hidden furnace closet room behind.