Groverarke Mine, Rookhope in Weardale.
Mining began in the early 1800s and was developed by the Beaumont Company in the 1810s. It produced fluorspar under the Weardale Lead Company and after WWII was one of the leading producers.
The mine closed in 1999. The buildings around vary in age and are now very badly damaged by scavengers, arsonists and time.
If you’d like to see how the inside of the mine looks these days (well, 2010) then some guys who are much braver than me have posted them online on their Mine Explorer website.