The Ulb River runs south out of the mountains between Isenmarch and the Dodenrike, before merging with the Elsa River at Boras and eventually flowing out to the Thunder Bay. The Elsa River is theoretically navigable as far as Sluggelse, but contrary prevailing winds and the Dodenrike death zone mean that wise sailors go no farther than Culmar on the bay coast. The Moss River runs from the southern mountains, defining the Shonerwald peninsula. Other major rivers include the Stora, Corsor, and Vasa in the south.
Before the establishment of the Empire, Isenmarch competed with Hanist over control of the Thunder Bay.
Isenmarch was the first human realm to successfully rebel after the Capitol Coup. The Luminal Bone Needle began reconquering it in October 509 and has pushed the borders of Free Isenmarch to the Moss River.
Shartharagathol and Urbazbbhund in the north of the Isen Mountains are technically part of Isenmarch, but can only be reached from Sharbhund by travelling over treacherous mountain passes that are frozen over between October and March. The Empire of Night administers them as part of Humma.