I love a very clear narrative and mystery is one of the most exciting elements of storytelling. Hidden passageways, underground tunnels, secret chambers a la Harry Potter, doors to inner realms. A dash of danger, a hint of intrigue, the sugary spice of imagination.
Tons of websites showcase various entryways. However, most seem to involve extensive remodeling, elaborate design and astronomical price tags. I thought this one though was very clever, seems DIYable and has delightful C.S. Lewis feel:
Entrance to children’s playroom through armoire! “This must be a simply enormous wardrobe!”
Now, an even more inexpensive design idea for creating illusion of secret room.