The tunnel hidden deep underground that links two ancient north Wales communities

manchestereveningnews.co.uk:

The challenging geography of Wales has always posed difficulties in linking communities or industrial sites. Such was the case when a passenger railway was planned to connect Bangor and Bethesda, supplementing the track that transported slate from Penrhyn quarry to Porth Penrhyn in Bangor.

The single-track more than four miles long was authorised in 1880, despite it requiring a climb of over 300 feet from its junction with the North Wales main line at Bangor and necessitating two viaducts and two tunnels to traverse rivers and hillsides.

Thomas Nelson and Co of Carlisle were commissioned to construct the route for the London and North Western Railway at an approximate cost of £70,000, reports North Wales Live.

There were two tunnels at Tregarth - No. 1 Tunnel at just 27 yards and No. 2 Tunnel, known as Tynal Tywyll, stretching for 297 yards.