Berwick-upon-Tweed is the most northerly town in England. It is closer to Edinburgh in Scotland than it is to Newcastle. As a border town, it changed hands more than half a dozen times from 1000 – 1482, ending up as part of England. Queen Elizabeth the First spent a fortune building fortifications around the town to deter invaders. I highly recommend a walking trip around the town walls and battlements.
I stayed in a guest house on the Parade Ground outside the Army Barracks (designed by Nicholas Hawksmoor, contemporary of Sir Christopher Wren). Many of the town houses are Georgian, almost 300 years old. And they have beautiful doors.