I was up at Croesor today, and we found that there is some sort of tunnel underneath the mill. Does anyone know what it was for?

I wondered whether it was for a shaft to drive saw tables etc. but why put it underground?

It's a bout 4ft square and runs the entire length of the mill, made from slate blocks. I never noticed it there last time.

It might be where the water wheel used to be situated.

I think it is, I set off down it a few months back when up there with Andy, Ian and Ant, but turned back when about 40 - 50m in as the roof didnt look to great and no one knew where i had gone.