The rather dramatically named Road to Hell is a great hill climb following the B4501 up from the outskirts of Denbigh towards Llyn Brenig. It is fairly long (11.5km) and features one particularly steep (17%) section. After a pleasant start, following lanes out of Denbigh, the road rears up steeply around the eastern flank of Foel Gasyth. A short descent which follows allows some recovery before the long undulating climb up to Llyn Brenig. The gradient isn’t too severe on this section but it is still quite energy sapping. It is possible to extend the route round to the visitor centre near the southern head of the reservoir.
The highest part of the route reaches the 400m contour; consequently during the winter months it is occasionally blocked with snow.
There are various starting points, depending on your intended route, but Denbigh or the Llyn Brenig visitor centre are obvious choices.