There was a field guide by the late Eric Holland published a few years ago. (Moorebooks?)
The levels are easy to find, park near the youth hostel.
Looking up over on the right hand valley is the arched entrance to deep level. There are other levels higher up.
Walking up the track on the left hand valley the track follows Levers Water Beck, you pass the water treatment plant and the track will take you right to Hospital Level. Its just a walk in same as deep level, but water up to your knees.
There is quite alot of exploration that can be done there without any special equipment.
If you want to take a look, try this:
http://wtp2.appspot.com/wheresthepath.htm It beats Google Earth hands down and it also uses National Grid not the stupid Latitude/Longitude 'Ship at sea' rubbish. You will be surprised how good this is, the satelite image is very clear.
Hospital Shaft is sealed at surface
My avatar is a poor likeness.