Originally uploaded for the Guesswhere UK group.

This is at Odin Mine (lead) near Castleton, Derbyshire.
This slot-like feature is Odin Gorge, which marks that portion of the Odin Vein which was completely worked-out at the surface, before being extensively mined underground.

Odin Mine is the earliest recorded, named, lead mine in Derbyshire, dating back to at least 1280, and possibly earlier - the Romans were thought to have worked the mine.