The Pit Wheel

The pit wheel is the first gear wheel driving the millstones. It is located on the same shaft as the waterwheel, and it's named a pit wheel because part of it is situated below the floor level in a pit. It is caged off to prevent accidents.

In the photo below you can see daylight where the shaft exits to the waterwheel.

In the photos below the pitwheel is being checked - you can see how just huge the wheel is and how narrow the pit is!