The small octagonal building behind Durham Cathedral is actually the Great Kitchen. It was built between 1366 and 1374 and is one of the best-preserved medieval kitchens in Europe. The structure is square on the outside but has an octagonal vaulted ceiling inside, with a central louvre for smoke ventilation from the fireplaces around the walls. Originally, it served to feed the monks of Durham Priory, their guests, and pilgrims. Today, the Great Kitchen is part of the Durham Cathedral Museum and houses the treasures of Saint Cuthbert.
This building is located behind the Cloister, next to the Refectory Library, and is notable for its distinctive octagonal rib-vaulted ceiling, which is architecturally similar to styles found in southern Spain.
 
Interesting facts..
The cathedral has a few. The Black Line for Women: Historically, women were barred from crossing a black line on the cathedral floor beyond the nave, as it was believed St Cuthbert did not like females and their presence distracted the monks. This rule applied to everyone, from commoners to royalty, including Queen Philippa in 1333, who was asked to leave when she crossed this line.
 
The Missing Statues of the Neville Screen: Behind the high altar stands the Neville Screen, a grand carved structure. It originally held 107 alabaster figurines that were removed and hidden by monks ahead of the dissolution of the monasteries under Henry VIII. Their fate remains a mystery, and they have never been recovered