I think it takes place every Saturday morning to afternoon, vintage shopping while having a great view at the Manhattan skyline from the East River State park. You will find lots of vintage shops and warehouses around this area of Williamsburg.
Erie Basin is a really wonderful little shop full of old, creepy and beautiful things, such as Victorian mourning jewelry (some with hair in it), Freemason masks from the 1900's, tiny children's rings from the 1700's, and all kinds of other treasures. It is really as much a museum as it is a store, and all of the items have a haunting and unique aura.