OverviewDuring the last Ice Ages, glaciers gouged out and deepened the Tawe Valley. With the retreat of the last glacier from the Swansea Valley 10,000 years ago, the Upper Clydach River was left perched high above the main valley floor. A spectacular waterfall formed at this point. Over the passage of time, the river cut back along its course to form a narrow gorge known locally as Cwm-Du-Glen. The gorge approximately 1km long follows the Upper Clydach River from the heart of Pontardawe, upstream to Rhydyfro. Here, a picturesque waterfall marks the termination of the gorge. Today Cwm du Glen and the Glanrhyd Plantation above are a designated local nature reserve. The main entrance is unusual in that it is located in an urban environment at the crossroad in Pontardawe.