For some big apartments, size is its own problem. This loft’s 5000 square feet leave the dark middle awfully far from the windows. We pushed the habitable rooms to the windows, packed the middle with storage, and ran a ring of circulation between the two zones. The end walls of the family room are giant etched-glass doors that slide into wall pockets to clear a path for the kids’ zip line. For the adults, there’s an acoustically isolated music room, a climate-controlled wine room, and sleek detailing.