With the Nantlle one. I think there's also an adit under the road.
there MAY be an adit under the road at nantile - but when richard and i [ UCET ] went for a recce and explore - we didnt find one
however we did find an engine shaft under the road - a very curious set up - located :
https://binged.it/2yHLKmG the hole is almost exactly the mid point of the 2 " b4418 " markers
bbelow the small reservoir - is obvious signs of disused mnine workings that ther farm has partialy " overgrown "
however - the retaining wall for the road " looked odd " - so we investigated - discovering a hole with an arched roof under the road - about 5m wide and 4m in
upon retuning to our vehicles - richard produced a book from his box of usefull things - and concluded that it was a capped engine shaft
there are several adits and stopes south of the b4418 - that we explored with mixed sucess - several required extra rigging and or a skilled climber - so we left them - but there are walk in adits - and one shaft that gave an easy 23m drop to nice workings
w started off at the eastern end - and the quality of explorable holes diminished once past the chapel [ plus we were geting tired - and losing the will ]
so yup - nantile is worth a look