"I wanted to build a piece that resembled a core sample of a city street. As though you took a street, dug it up, and lifted it straight off the earth. "Canal St. Cross-Section" is a combination of five major pieces built into one box. There's a street scene on the top with a subway entrance on the corner. Looking down into the subway entrance, you are led to the two subterranean levels of the piece, both of which have intersecting cross views visible through the small windows on the sides of the piece."
More details about how he constructs these toward the bottom of the FAQ.