There is accessible underground stuff if you go higher up. You can enter a level (with false floor), and abseil down one level. I forget what happens next, whether there is possibility of a 2nd abseil or not.
I also forget what happens if you try to get along the level further. It is heading directly towards Britannia Copper Mine - maybe that is where the connection is!!
The mine is basically a big stope, with various levels. We considered going further up, but have yet to do so.
The adit is fairly obvious by the different coloured spoil outside. Quite a challenge to actually get to it as I recall!!
Chris.