An underground storage area(u)
This is a storage area for wood and peat. The wood is chopped into arm-length logs and stacked in neat, waist-high cords along the walls. The peat is piled in the center of the room. There is enough fuel here to keep the castle's chimneys and stoves going for several months. A stairway runs around the wall, leading back up to ground level.
The only obvious exit is up.