From English Heritage website.
Guided tour: Grime’s Graves Neolithic flint mines
Grime’s Graves is one of only handful of Neolithic flint mines in Britain, and the only one where you can actually go down into one of the 5,000 year old mine shafts. The guided tour will be on Sunday 27th June 2004 and will include a spot of DIY fieldwork! Please note that places on this tour are reserved for English Heritage Members only. For further information about the tour, contact Pete Topping in English Heritage’s York office on 01223 582 700 or e-mail [email protected].