I've been in the Sunderland-Durham area many times, and finally I got around to seeing these ruins. Remote and lost in a bend of the River Wear, these are the ruins of Finchdale Priory. I say ruins, but they are in fairly good condition, so you get a good idea of the size of this thirteenth century Benedictine abbey. It was founded by monks from Durham Cathedral, as a retreat to escape attacks from pirates and vikings. The name reflects the fact that a noble from the early twelfth century, Godric of Finchdale, was buried here. The monastery's story ended with the Reformation of Henry VIII.
Today the site is controlled by English Heritage, but the ruins are on private land, so you have to pay £3 to access the site.