One of a number of adits opening directly below an old leat bed running parallel to the north bank of The River Walkham between Grenofen and West Down.
Noticed this one a few years ago, initially as a Rabbit warren sized hole issuing water below the leat bed.
If you Enter (at what i believe to be original floor level) you are met with a sharp grade up over fall material into a small cavern of around 15-20 feet in height (collapsed stoping?) Beyond which the top of the flooded adit is visible.
We did at one stage manage to syphon enough water out to lower the water to chest height and venture further in, following the adit for approximately 150 feet. (rough memory). The adit had some interesting formations along the high waterline and gradually the clear water got thicker with ochre until it became very difficult to progress.
We got as far as a kink in the adit where we could see the ochre rising higher up the walls into the distance and reluctantly turned back, we never did get the water level as low again, so never got the chance to push any further.
I am unsure whether this is a trial adit or connected in some way with the shaft and workings on the Downs above. Information on the mines and ruined buildings along this side of the river seems to be hard to come by.