The Clydach Gorge (also known as Cwm Clydach) is a steep-sided valley in south-east Wales down which the River Clydach flows to the River Usk. It runs for from the vicinity of Brynmawr in Blaenau Gwent eastwards and northeastwards to Gilwern in Monmouthshire. The Gorge was one of the first locations in the region to be industrialised though it still retains its natural environment. It has long been an important transport corridor between Abergavenny and the lowlands of Monmouthshire and the northeastern quarter of the South Wales Coalfield. It is now exploited by the A465 Heads of the Valleys trunk road which runs between Abergavenny and Swansea and which serves the Heads of the Valleys sub-region. The Gorge is included within the Brecon Beacons National Park and is a tourist destination in its own right, with facilities including a picnic site, waymarked footpaths, the National Cycle Network and car parking alongside the River Clydach, easily reached from the Heads of the Valleys Road. It includes Smart's Bridge, a cast iron bridge and the remains of a late 18th-century ironworks which are now a Scheduled Ancient Monument. There are also limeworks. Settlements The industrial town of Brynmawr sits at the head of the gorge and the large village of Gilwern sits at its foot in the Usk valley. Although development along the gorge and its sides are semi-continuous, the linear settlements of Clydach (now Clydach South), Blackrock, Cheltenham (now Clydach North) and Maesygwartha can be distinguished along the roads between Brynmawr and Gilwern, mainly to the north of the river. The settlement of Llanelly Hill occupies the northwest hilltop of the gorge. Industrial heritage sites Ironworks Llanelly Furnace and Forge The Hanbury family of Pontypool established a furnace and forge here (OS grid ref SO 236140) in the sixteenth century though nothing now remains of them other than parts of the masonry dam of a pool connected with the water power used for the forge. Wrought iron was made at the furnace from cast iron using charcoal. A tinworks also operated at this site at one time. Clydach Ironworks The Clydach Ironworks was the most significant ironworks developed in the Cwm Gorge. The Ironworks were constructed around 1793–95 after coke had been introduced as a fuel for blast furnaces. By 1841 the works was responsible for the employment of more than 1350 people though many of this number were associated with