If you have time to visit only one Hadrian's Wall site, Housesteads Roman Fort, Britain's most complete example of a Roman fort, is your best bet. It includes long sections of the wall, an excavated fort, and a new visitor center with a collection of artifacts discovered at the site and computer-generated images of what the fort originally looked like. The fort itself is a 10-minute walk uphill from the parking lot (not for those with mobility problems), but the effort
is worth it to see the surprisingly extensive ruins, dating from around 125AD. Excavations have revealed the remains of granaries, gateways, barracks, a hospital, and the commandant's house. The northern tip of the fort, at the crest of the hill, has one of the best views of Hadrian's Wall, passing beside you before disappearing over hills and crags in the distance.