There are a number of large statues of a faceless black monk, just outside the Short Leg Gate Tower gate that separates the upper town on Toompea Hill (where the rich lived) from the lower town. This gate was shut every night to keep the lower classes and some of the local ghosts away. The black monk was one of the ghosts that is said to inhabit this part of town.
This particular version of the black monk sits on a platform part way up the wall and seems to stare down at visitors coming through the gate.