The National Coal Mining Museum, Caphouse Colliery, Wakefield (01924 848806) is now encouraging participation of small, groups of relatively fit persons in a tour of the underground workings (the 'visitor' mine) exiting via the second exit (Conveyor Drift), which is not normally open to the public, but which is nevertheless inspected daily. You will need to book in advance, and there IS a charge for this service to cover staff costs, currently £30.00 per group plus £3 per head for your (refundable) pit check. I kept mine.
This trip is well-worth doing; our guide Steve Oxley, had us in STITCHES at times and was most knowledgeable about Caphouse in particular and coal mining in general.
The 600M walk out of the Drift, ascending 140 vertical metres, is impressive to say the least, and most heartening to see an ongoing process of maintenance and repair, and continued use of the NCB machinery.
Strange to emerge on the surface NOT soaked through and covered in ochre (okker they calls it)
enjoy....