Travs
If you want a challenge, try this:
http://users.aber.ac.uk/dip/nym/skyline.htm
one word: tussocks!
In that area, you can park at Nant y Moch and then go south onto Y Garn (no path, but follow the reverse of the Nant y Moch route from CP9), then follow the ridge/fence to Pumlumon Fawr, Pumlumon Arwystli, pop down to the Source of the Severn, then back up and drop into the Afon Hengwm, following it back to Nant y Moch.