You are looking for a small Lock-N-Lock "medium" waterproof container hidden in the Williamstown "Town Recreational Area Nature Trail".
The trailhead is located at the end of Arnold St. There is no designated parking area so you have to park on the street, just be mindful of the numerous "No Parking" signs.
This stash was started with a bunch of goodies (for young and old), so please try to trade equal or up to keep a good supply.