I always wanted a secret bookcase/door in my house. So when the door to the space under the stairs in our house needed replacing because the previous owner had put a giant hole in it for some reason, I knew I had my chance.
I used a 2 x 6 to carry the weight of the hinges. Five 1 x 6’s served as the shelves and top. I was nervous to make the bookcase any wider, for fear the the extra width would bring too much extra weight, and was not prepared to weld a steal frame.
I got a 1 x 10 for the far piece because I wanted to install it on an angle, cutting the shelves as necessary, so the corner of the bookcase wouldn’t catch when opened. I made the angle way more dramatic than necessary, but whatevs. It’s fine. The back is a 3/4″ thick piece of plywood, which provides the case with some extra structure. Then I trimmed the whole thing, making sure to cut the pieces near the hinges at an angle so they wouldn’t catch; sanded it some; and used at least a tube of caulk to cover up my myriad of small mistakes.
Five hinges carry the extra load. I had them leftover from when I refinished all the interior doors and replaced all the hinges. A couple of magnets on the trim holds the case to the jam, and I picked up a cool handle on Ebay for more convenient opening/closing, but I didn’t get that on till after I took these pictures. I painted the whole thing white, and the back of the case green to add a sense of depth.