It has its sources in the Ulakhan-Sis Range and flows roughly northeastwards across the Kondakov Plateau. Leaving the uplands, it crosses the Yana-Indigirka Lowland tundra, part of the greater East Siberian Lowland. It flows first in a roughly eastern and then, more than halfway through its course, in a northern direction. Its mouth is in the East Siberian Sea at the western end of the Kolyma Bay. The Sundrun River freezes up in early October and remains icebound until June.