Constant change. As the old joke goes, "New York is an amazing city.... its going to be FANTASTIC when it's finished!" Of course, it will never be finished, constant tearing-up, rebuilding and alteration is a big part of its allure.
Day 4 - A sidewalk on on Gansvoort Street, cobbles, tarmac, cement, concrete, hardboard, duct-tape, utilty line markings. History displayed like the rings of a tree.