For D.C. resident Nicole Buell, a bookcase that concealed a doorway solved a design problem. In her 540-square-foot condo, the doors to the only bathroom were in her bedroom and the living area. The living-area door left too little room for pictures or bookcases. "It just wasn't a good use of space," Buell said. Walling over the door was an option, "but," she said, "I didn't want guests to have to go through the bedroom to get to the bathroom."