The cesspit
Image: A cesspit with a iron gate with lock on the other side.
You decide to survey the surrounding area by following the ridge of the gorge. After traveling for several hours you find yourself on the backside of the castle where you encounter the entrence of a secret cave. You enter the cave which takes you futher and further down into the mountain until you reach a large room with a gigantic cesspit that reeks like a toilet. On the opposite side of the cesspit, filled with excrements and feces, there is iron gate with a large circular dial lock, with numbers on, that lies half submerged. The gate was probably meant for a way of regulating the sewage from the castle.