Of all the places where Hadrian's Wall still behaves like a wall, Walltown is one of the most dramatic. The masonry rides the crest of the Great Whin Sill, a sheet of hard dark dolerite that pushed up through the surrounding rock about three hundred million years ago and then weathered into a line of cliffs facing north. The Roman engineers simply put their wall on top of the cliff, so the stones rise and fall with the crags, dipping into gaps the locals call nicks and climbing out again. Stand up there on a windy day and look north towards the empty country of Northumberland and you understand exactly why they chose the line.
The quarry is a later chapter. In the nineteenth and twentieth centuries the same tough whinstone was quarried for road stone, and the quarrymen took away a good chunk of the crag and the wall with it. When the work stopped the hole was landscaped into a small country park with a pond, reeds and picnic tables, and it makes a good place to leave the bike and walk west along the best-preserved stretch. Just down the road at Carvoran is the Roman Army Museum, and nearby the ruins of Thirlwall Castle were built partly of stones taken from the wall.
The riding is the Military Road, the B6318, at its finest, though here it runs a little south of the crags. It is long, straight in sections and full of dips and crests that hide oncoming traffic until the last moment. In summer you will share it with campervans and walkers crossing to footpaths, so keep your speed honest and watch the lay-bys. Westwards it drops towards Greenhead and the A69; eastwards it heads past Cawfields and Housesteads, where the wall views get even better. Wind is the constant up here, often strong enough to push a bike across the lane.
Haltwhistle, a few kilometres away in the South Tyne valley, has fuel, shops, cafés and a station, and it likes to call itself the centre of Britain. Brampton to the west also has fuel, and Hexham is the nearest bigger town if you need a proper supply run. Facilities at the quarry park are basic, so bring water and expect the weather to change at least twice before you get back on the bike.