Just a thought , if the only access to this quarry is to abseil into it
How did the quarrymen get to work or get the slate out ?
Often access now isn't the same as access then ;)
There are tunnels through to the pit behin and the pit in front (which therefore goes under the road) however that one pops out in mid air these days!
I think I'm correct in saying all the three main pits on the lower part of that hillside where connected by tunnels. You can still find these tunnels although sadly the longer one is collapsed.
The whole hillside is definitely well worth a look. From Glynrhonwy Isaf and the Llanberis bomb store (sadly no longer accessible) to Cefn Ddu (with its own very impressive tunnel) on the ridge.
The bridge in question? I honestly do not know. I was just going off what I had been told. Certainly you don't need to cross the bridge to get to the back of the pit - the trench it crosses does not run all the way across the pit. It may be original, it may be a movie prop. If original why is it so hefty (there are movie scenes of vehicles on it). If a movie prop why was it left behind when everything else was remvoed. It needs a good clear archive photo of the pit to prove one way or the other :)
As an aside it would be interesting to know how they got the vehicles and construction materials into the pit for the movie set.
my orders are to sit here and watch the world go by