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.
An awesome, and sometimes free, ferry that links Manhattan at the Financial District to Ikea in Brooklyn via Red Hook. Very great views of the city and if you end up having to pay it's redeemable for a monetary discount towards an Ikea purchase. I think of it as a treat and an investment.