The bookcase bed, and the heart of the home?

This would certainly be fun in a smaller flat - who needs a sofa bed for guests when you can accommodate them with a bookcase bed!!

Not sure I understand the workings of it fully - apparently there's 4 sections to make it into a double, and 2 for the single, but I can only see 2 parts. I assume there's a double layer of mattress, one hidden behind the other, when it's stacked against the wall?



And I also want this done in my house...unfortunately, I think I'm a teensy bit short of the space needed!!