Behind the door to the Great Hall is a large metal cover. It may be the entrance to a small bottle dungeon (sometimes called a pit prison).
This was a structure with a narrow opening and a wider chamber below it, like a bottle. People were imprisoned there and it was virtually impossible to escape without outside help. The torture involved was that you could hear everything going on but could not join in or see what was happening.
There are examples in Dundonald and St Andrew’s Castles.
We have not been able to excavate this chamber in Portencross Castle yet. It is expensive as it may have archeological materials inside. Excavation might also affect the structure of the Castle. Perhaps we will be able to excavate at a future date.