What was in a Keep in a medieval castle?

Answer 1

The word keep was not used until after the medieval period, so in that sense medieval castles did not have keeps.

The medieval term was donjon or donjun (in Anglo-Norman French), which meant the main defensive tower in a stone castle. Every castle was different, so the donjonmight be centrally placed or offset to one end, or even part of the external circuit wall (the curtain).

Norman donjons were generally square or nearly so, and with a storage area on the ground floor, accessible only from inside. The first floor included the entrance, reached by an external stair of wood or stone; above this might be the chapel and main hall, with private apartments on the floor above. At roof level were battlements and small corner towers. Inside would be a deep well to provide water.

Some donjons were circular, others made with many sides.

The whole concept of a "final refuge" in the donjon if the rest of the castle were captured proved to be flawed; perhaps the attackers could not get in - but neither could the defenders get out, so it effectively became a prison. In the long term the defenders could be starved into submission.