This is the Evo Triangle, used by Evo magazine for alot of their road tests:
It's just south of Denbigh, and incorporates parts of the A5 and A543 near to Betws-y-Coed.
There's more information, and pictures on the Piston Heads forum here:
http://www.pistonheads.co.uk/gassing...p?h=0&t=304051