A long river that runs through Burncastle. Don't follow it. There are dozens of tiny tributary streams that descend from it and run off into the remote wilderness, and all of them look exactly like the main river until, following them, you start to consider that you should've hit the main road at some point. Getting lost is beyond simple.

Deirdre's house is set directly on the river, surprisingly enough. South from that is the academy, and further south than that are the old factories and the swamps.