When Christian Schallert bought his apartment, his mother was appalled. You have to climb 100 steps just to get to the apartment. When Christian moved in, there was an old mattress sitting on the floor, left behind. The apartment had no ceiling, old paint, and needed to be completely redone. To top it all off, the apartment is only 258 square-feet. But Schallert knew exactly what he wanted to do with it. Upon first glance, the remodeled apartment looks completely empty. But, when he starts opening the cabinets hidden in the walls, it becomes clear that the Barcelona apartment has...