@Alan Clogwyn I presume you know this stairway?
For those who don't this was taken from across the far side of the mine. The stairway runs from botton right to top left of the shot. This is less than a third of the whole. It winds it's way to uper levels of the mine high on the hillside overlooking Llanberis. There is something like 700' drop off on the right hand side. This used to be the regular way to work for miners when the mine was in operation. No HSE rules here.
The bottom 20 steps or so are clear and easy. After that the steps become irregularly spaced and are covered with varying amounts of detritus. And it was wet. We thought about going up, but
@Mr Perceptive just didn't fancy trying to get down again. Neither did I.

Stairway to Heaven by
mickledore on Talk Photography
I've been up (and down) several times before in the dry. It's worth persevering because you eventually come to the Australia Level cutting sheds. These are some 2000' above the valley floor and how they got all this machinery up there is a mystery.
Auatralia Level cutting sheds. by
Frank Yates2010, on Flickr
Talking of Australia, it's 4-0 this year. Whoopeeeeee!