Really Fun Library Slide - Architect Moon Hoon designed the Panorama House in South Korea, which features a multi-functional library. A wooden slide (used by the adults in the home, too!) is flanked by stair step bookcases.
DIY Cardboard furniture That doesn't look like it's made from cardboard! We've had some great posts on cardboard furniture you can buy that doesn't LOOK like cardboard, but most DIY options resemble the brown recyclable stuff.
We've used a similar corner shelving unit to create space in a small 7 by 9 ft room. It's a great, easy shelving solution for small spaces (although installing it was a bit tricky as the walls weren't plumb.