Trefil is a small village in the county borough of Blaenau Gwent, south Wales. It lies at the top of the Sirhowy Valley, three miles northwest of Tredegar. The boundary of the Brecon Beacons National Park lies one mile to the north of the village.The village is sited in the bottom of a broad valley which cuts through the moorlands between the Heads of the Valleys Road and the Dyffryn Crawnon valley to the north. At a height of 400m above sea level it is one of the highest villages in Wales.