I'll second the Snake Pass being between Glossop and Sheffield – used to drive over it regularly on business trips. The Llanberris is a good way from Llangollen – not so far from Betws-y Coed though.
The pass at Llangollen is the Horseshoe Pass.
Also if you get to Llangollen look out for the Froncysyllte aquduct and the modern equivalent viaducts on the A483, wouldn't have fancied a brikkies job on any of them.
Llangollen is about half an hour in the car from where I live
Keith.