Tynal Tywyll, Lon Las Ogwen – Dinas Railway Tunnel

Dinas Tunnel – the former branch-line railway tunnel between Tregarth and Bethesda, known informally as Tynal Tywyll (dark tunnel).


14 May 2017


Dinas Tunnel, Lon Las Ogwen, Tregarth
SH 60818 68185; 53.19247°N, 4.08473°W


In 1884 a four-mile-long, single track branch line of the London and North Western Railway (LNWR) from Bangor to Bethesda opened to passengers, linking to the Chester and Holyhead main line just outside Bangor. The route included Dinas Tunnel, a 297-yard-long (272 m), single-bore tunnel approached from the Bangor (northern) end through a sheer-faced rock cutting. On exiting the tunnel at the Bethesda (southern) end, the track crossed the Ogwen river over the Bryn Bella Viaduct. Increasing competition from buses led to the closing of passenger services on the branch line in 1951, with the line finally closing to all traffic in 1963.

In 2016 Gwynedd Council set aside £200,000 and secured an additional £230,000 from the Welsh Government in order to develop the disused tunnel so as to open a new section of the Lon Las Ogwen ‘multi-user’ path. This 11-mile-long cycle route follows parts of the trackbeds of the narrow-gauge Penrhyn Quarry Railway and the standard-gauge LNWR branch line and has until now been interrupted by a mile-long detour around the tunnel by road.

The development work was carried out by Trawsfynydd-based contractor G H James and involved: securing the rockface in the cutting; lighting the tunnel; installing safety railings on the viaduct parapets; and clearing and surfacing the path. The new 800-metre-long section of the route opened in May 2017.

Further Reading

All posts about Dinas Tunnel;
Lon Las Ogwen


Dark Places

Caban, Dinorwic Quarry · Fron-boeth Quarry Tunnel, Cwm Croesor · Llanberis Bomb Store · Moel Faban Quarry · Dinas Railway Tunnel, Tregarth · Braich Tunnel, Dinorwic Quarry

‘Dark Places’ on YouTube

Blaen-y-nant Molybdenum Mine
Coed y Dinas Copper Mine
Croesor Quarry
Cwm Ceunant Copper Mine
Dinorwic Quarry
Dorothea Quarry
Fron-boeth Quarry
Glyn Rhonwy Isaf Quarry
Caseg Valley
Moel Faban Quarry

Rhosydd Quarry
Tan-y-garth Arsenic Mine
Dinas Tunnel, Tregarth
Dolbadarn Castle
Roughcastle Tunnel, Falkirk
Llanberis Bomb Store
Llanddulas Jetty
Penrhyn Quarry
ROC Llangefni
Coast Artillery School, Great Orme