Dolgellau (/dɔːlˈɡɛli/; Welsh pronunciation: [dɔlˈɡɛɬaɨ]; formerly anglicised Dolgelley or Dolgelly) is a market town in Gwynedd, north-west Wales, lying on the River Wnion, a tributary of the River Mawddach. It was the county town of Merionethshire (Welsh: Meirionnydd, Sir Feirionnydd) before that became a part of the county of Gwynedd. Dolgellau is the main base for climbers of Cader Idris.