Drains

It is pitch black. You are likely to be eaten by a grue.

Or an albino crocodile, gelatinous icosahedron, mutated testudinal humanoids, giant radioactive goldfish or, if that hysterical fellow from the water company is to be believed, a minotaur. Nobody knows how they got there and the Professor assures everyone that they were there long before his family moved in.

It is unknown just how far the drains go. Some villagers believe they feed into a vast underground tunnel system carved millennia ago by Shambalan priests who took a wrong turn on their way to visit Egypt. Others say they are repurposed tunnels that once stretched the several miles between the old folly and the original manorhouse, now terminating in a long-forgotten septic tank. Nobody has dared to find out.