Lanercost Priory is a handsome Augustinian ruin east of Carlisle, close enough to the old Scottish border to have had a hard life. Founded in the 12th century and dedicated to Mary Magdalene, it was repeatedly caught in cross-border warfare; Edward I stayed here for months in 1306 while ill, and Robert the Bruce's forces raided it a few years later.
The surviving church and red sandstone arches make it one of the best monastic ruins in this part of Cumbria. It pairs well with Hadrian's Wall sites nearby if you have a car.