There is no underground up at the main site, access is below the Wemyss dressing floors by a shaft down to the adit.
The route to engine shaft is not yet open I'm afraid, but still plenty to see.
Be sure to replace the manhole covers on the adit shaft properly when you exit please. Also, if you dont do the stope swims water is wader depth max.
Up in the 14, the obvious crawl is a bit horrible towards the end, also the fall area which blocks the 14 further inbye is an unstable area so take care.
Good explore.
My avatar is a poor likeness.