The B6138 claims to be the longest continuous gradient in England, climbing 968 feet over 5.5 miles from Mytholmroyd (and the A646) in the Calder Valley to the heady heights of Blackstone Edge on the A58.
The road is liable to closure in winter and a rotating prism sign on the A646 informs traffic of this. The gradient is shallow but it does go on and on, as the road twists past stone terraced houses and through wooded areas on the valley sides. As it passes through Cragg Vale it starts to open out and reaches the moors and the eventual end of the gradient. Here the 30 mph limit is replaced by one of 50 mph and the route becomes a fast road across very bleak peat land. It is safe to say that if your vehicle comes off the road up here you won't be getting back on it in a hurry. A small junction at Sykes Gate provides access to Sowerby village via some very narrow country lanes, while the B6138 blasts ahead with some deceptively sharp turns.
After a few more miles the road enters Lancashire and on the northbound side a 1980s "West Yorkshire: Working for Peace" sign still survives. To the right is a reservoir which frequently flows over the stones and onto the road – which, if it is freezing outside, causes a multitude of problems and an inevitable road closure. The junction with the A58 is directly ahead, the speed limit returns to NSL, and a simple Give Way ends the B6138 in one of the bleakest spots on the southern Pennines, despite its being covered by a forest of National Grid power lines.