- Level
- The lowest of three, underground
- Holds
- Cisterns, magazines, tower bases
- Also
- Passages the dossier calls secret
- Decides
- How long a siege can be survived
The lowest of the castle's three levels is underground: magazines, storerooms, cisterns, the bases of the defensive towers, and a set of passages that the dossier calls secret.
The cisterns are the point. A castle on a rock above a river has the maddening problem that the water is right there and completely out of reach — going down to it under siege is going down to be killed. So the rain is caught instead, and kept below the rock where it cannot be fouled or evaporated, in cut chambers that hold enough to outlast the season an army can stay in the field.
Some of the underground passages are said to have run down to the river itself. That claim is repeated in the published accounts and is not something this site can confirm.