Strand is a castle of books. It claims 2.5 million new and used books, across 18 miles of shelves, cared for by 200 employees—so set aside a couple of hours. Plenty of art books and good prices. Get your healthy huff of that old book smell.
One of the only things I enjoy about taking the subway these days is seeing the defaced ads on the L train. Whether it's random chance, high schoolers or street artists the result is always good.