As far as I can remember, near the top of one of the spoil tips there is a level that has been partly bulldozed. However there is a hole with some rope that you can hand-over-hand down into the workings which take you through a pit with some tunnels to the main workings.
The drainage level into Hodge Close is worth a look if you are nearby, it leads to all sorts of workings and it opens out into the massive pit. You look like an ant down there to all of the tourists looking down from the edge above.