The Frozen Road is a frigid, slow-moving river that arises from the Tusk Mountains in the Realm of the Mammoth Lords, continues west through Irrisen for 200 miles and then turns south and pours into Glacier Lake. It acts as a 200 miles long border between the Irriseni provinces of Feyfrost in the north and Thronehold in the south. Its last 50 miles long segment forms the border between the provinces of Bleakmarch in the west and the Thronehold in the east. Floes of ice move westward downstream all year, often blocking river traffic for miles. A large number of ice cleaving teams out of the town of Trezira patrol the river in 3-month tours along all its length breaking up the ice blocks. Frozen Road is populated by numerous fish, though more dangerous creatures live in or along the waterway, including many wild feys unwilling to live in Chillblight.12
For additional as-yet unincorporated sources about this subject, see the Meta page.