SBB[24]/CyB{13/16} - Well

Apart from the strategic value of location this hillock had another advantage - a water supply.
Not sure if this a true well, an enclosed spring or merely a cistern collecting rain water draining from within the castle.
It looks less than salubrious to modern eyes, but frequent drawing of water would prevent stagnation, even if it is just a cistern.
The fence is very necessary, as the ground level on that side is almost level with the top of the wall - and there's nothing to help you climb out.