The North Trench

A deep-set canyon that falls at a nearly 90-degree angle, or steeper in places. At the bottom, there isn't even any shoreline, the cliffs descending straight into the powerful flow of a rapid-flowing channel.
Impossible to cross directly across, a single bridge has been built across it, with the owners of both sides guarding them vigilantly.
On the northern side, the river forks into more than a dozen different tributaries that carve up the peninsula to the north. These rivers retain the speed and power of the trench, making them all dangerous to traverse for even skilled sailors. Even a moment of inattention or relaxation can mean you get ground upon the rocks.