Lots of mines near Coniston my friend, most of them require a fair bit of technical stuff. You're best contacting CATHMS
http://www.catmhs.org.uk/ Some of the famous trips throughout the coppermines include the Paddy End through trip, go in at Levers Water mine, descend lots of stopes, some of them filled with huge collapses, end up at Hospital Level. I would check with CATMHS before doing this, I think the top entrance might be locked.
There's Fleming's to Taylor's Level trip, different valley, same mine system. Drop from the wet Fleming's level, descend lots of stopes to Taylor's, see the Blue Cascade and wonder over the old stemples back to day, again very technical.
Some of the levels such as Hospital/Grey Crag level, Deep Level, Cobbler's Level, Taylor's Level can be done without SRT, though many of these would need cowstails.
Also many slate mines in the area, most of them small chambers/cave workings, open quarries extended into the mountainside along the slate bed, though the Moss Head and Spion Kop workings beneath the summit of the Old Man of Coniston are safe and fascinating to visit, lots of remains there. Not very complex but still big for Cumbria
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