“Much of what distinguishes the expanded Walker won’t even be seen by visitors. The complex sits atop an underground labyrinth that includes a 670-stall parking ramp and a network of art storage rooms, frame shops, photo labs and corridors linking the old and new buildings. Huge elevators will carry art from an enclosed loading dock at the south end of the complex to a 14-foot-tall subterranean corridor that parallels Hennepin Avenue. From it, art can be trollied into storage rooms or elevated nine or more stories to the top of the original Walker, one block north.”