Due a large number of F'wits having been in and around there are loads of marking which do nothing to help. Try Darkplaces • Portal, a lot of the guys on there are local to the bathstone mines.
Route finding can be tricky if you get off of the main haulways.
Surveys used to available from the quarrymans arms pub. not sure if thats still the case, there are three A3 laminated pages, northern, central and southern. (I've got a set if want to pm me) These only cover the unmodified areas, beyond the barbed wire and red door is another thing entireley
Box has been pretty well sealed due to teh idiots visiting, least of all the 4 guys that got lost in there during lockdown & had every emergency service available out!
You may of found an entrance as there was still a few sneaky ways in.
The pub certainly dont give out maps or keys now, they used to but that was before Hanson took control & sealed it.
Also as Im sure you are aware if u get to the red door of the bunker you will undoubtable have the police waiting for you on exit.
Essentially yes dont go without someone knowledgeable & a good sense of mine navigation, its fairly easy to navigate once you know what you are doing but with over 60m of tunnels there the consequences of getting it wrong are serious.