The Mawddwy Railway was a rural line in the Dyfi Valley in mid-Wales that connected Dinas Mawddwy with a junction at Cemmaes Road railway station on the Newtown and Machynlleth Railway section of the Cambrian Railways.

Dinas Mawddwy is a town in the community of Mawddwy in south-east Gwynedd, north Wales. It lies within the Snowdonia National Park, but just to the east of the main A470, and consequently many visitors pass the town by. Its population is roughly 600. The town marks the junction of the unclassified road to Llanuwchllyn which climbs up through the mountains to cross Bwlch y Groes at its highest point, the second highest road pass in Wales. This minor road also provides the closest access to the mountain Aran Fawddwy and is the nearest settlement to Craig Cywarch.