Haltwhistle sits in the Tyne Gap, the low cleft where the South Tyne and the old Carlisle road squeeze between the high moors of the north Pennines and the Whin Sill ridge, and that gap is the reason the Romans cared about this ground. A temporary camp is exactly what it sounds like: a ditched and banked enclosure thrown up for a night or a few weeks by an army on the march or on building duty, then abandoned. Most were ploughed flat long ago and now show only as crop marks or faint corners in a pasture, so go in expecting a field, not a ruin. What you get is the story, and the story is good.
Hadrian's Wall was begun around AD 122, and the legionaries who built it needed somewhere to sleep while they quarried, hauled and laid stone along this stretch. Camps like this one are the scaffolding of that effort. A few minutes away the real thing is easy to find: the Wall itself, the ditch-and-mound system called the Vallum behind it, and the forts and milecastles strung along the ridge towards Housesteads and Vindolanda. The Roman Army Museum near Greenhead is the sensible rainy-day stop, and Walltown Crags is where the Wall climbs most dramatically.
For riding, the lanes around Haltwhistle are narrow, hedged and often bumpy, with the occasional cattle grid and a fair number of sheep with opinions. The Military Road, the B6318, runs along the line of the Wall further east and is the classic run, though it gets busy with walkers' cars on summer weekends. Go early, or in the long light of a June evening, and the ridge views north into Northumberland are enormous. In winter the same moorland can ice over without warning, so treat any shaded dip with respect.
Haltwhistle has a few thousand people, a main street with cafes and a bakery or two, and petrol, so it is the natural place to top up and eat before you head out. The town likes to call itself the centre of Britain, a claim based on some creative measuring between the coasts, and it will cheerfully tell you so. If you need a bigger shop or a wider choice of fuel, Hexham is about twenty-four kilometres east along the A69, and Brampton and Carlisle lie to the west.