Pen Twyn Glas is a top of Pen Allt-mawr in the Black Mountains in south-eastern Wales. It lies in between Pen Allt-mawr and Mynydd Llysiau.
The summit is merely a grassy bump on the ridge marked by a pile of stones.Nuttall, John & Anne (1999). The Mountains of England & Wales - Volume 1: Wales (2nd edition ed.). Milnthorpe, Cumbria: Cicerone. .
References
External links www.geograph.co.uk : photos of Waun Fach and surrounding area