There are a lot of fascinating places to visit when you are in the area. You may wish to have a day off from walking. Here are some of the places you could go to or things you might like to do.
Vindolanda and the Roman Army Museum
Not far from Haltwhistle are 2 sites owned by the Vindolanda Charitable Trust. More information here
There are a number of properties managed by English Heritage in the area. Here are just 3:
Birdoswald Roman Fort
Chesters Roman Fort and Museum
Belsay Hall, Castle and Gardens