N51 46.198 W3 46.383
Just off roundabout into industrial estate in Gurnos (actually slightly nicer than it sounds) which is on A4067 kinda half way between Neath and Brecon.
Either take Junction 43 off M4, the heads of valley road A465 and then across to Abercrave (passing BMW off road grounds) and back down, or J45 and up A4067, or have fun in Brecon national park before coming down.
I'm going to go A470, A4215 then down A4067 - all excellent biking roads. Watch for police camera vans just before and just after Pen Y Fan.