Assassin's Creed: Brotherhood

There is a well by the front of the horse stable nearest to the Thieves HQ that gets unlocked early in sequence 3. This is just one possible location as you can get this at any well you find. Hit the "R1" button to bring up the weapons menu select the money pouch near the bottom. Then walk up to the well and press the square button to throw money into it. You need to have a minimum of 10 florins to do it.