The Town Wall. The Durham Tower, built in the late 13th Century, is one of the seventeen wall towers.
The current Durham Tower plaque is http://openplaques.org/plaques/43439. The plaque currently in the location shown on the map is http://openplaques.org/plaques/43438.
Plaque is now missing
Rear of Stowell Street, Chinatown, Newcastle upon Tyne
Google Streetview
OpenStreetMap