We had to pass under this viaduct on the way to see Llanberis Waterfall. The path ran down the back of some buildings and didn't look like it was going to lead anywhere but we had it on good authority from a local restaurant, that if we took the lower path we would be at the foot of the waterfall. All signs for the waterfall point uphill, but following the lower path alongside the river we did indeed find a stunning waterfall - photo will follow. The train from Llanberis up to the summit of Snowdon crosses this viaduct on its journey. Best viewed on black.