Cwm Llwch

A walk up to a classic glacial cirque containing Llyn Cwm Llwch beneath Corn Du and Pen y Fan.

OS grid ref SO 002220 (lake)

These two hills and their connecting ridge, once referred to as Cadair Arthur, are built from Brownstones Formation rocks sitting atop Senni Formation rocks and all capped by the harder-wearing sandstones of the Plateau Beds.  Impressively steep slopes drop from the airy summits to the lake occupying the glacially excavated hollow.


  • Old Red Sandstone (Devonian); Senni Beds, St Maughan’s Formation, Plateau Beds
  • Quaternary; glacial cirque & lake, moraine


  • OS Landranger 160, Explorer map OL12
  • Geological — BGS 1:50,000 sheets: 213 ‘Brecon’


  • Walk features in various guides


  • Free ‘informal’ car parking in National Trust-owned field at end of tarmacked road at SO 006244
  • Entry: free


  • Mostly rocky, uneven paths; 300m / 1000’ ascent to lake; open country beyond halfway point; mountain environment — take care!

Transport links

  • By car — by minor roads from Brecon or Libanus
  • By train — nearest stations at Llandovery, Merthyr Tydfil and Abergavenny — see Traveline Cymru
  • By bus X17 & X43 services — nearest stop is on A470 at Libanus — see also Traveline Cymru

Other Geopark attractions nearby