The Sellen Passage is the great river trade route that connects the inland nations of central and eastern Avistan with the larger, richer metropolises along the Inner Sea. Its northbound journey begins at the city of Absalom and heads straight for the Taldan port of Cassomir at the mouth of the mighty Sellen River. There it transfers to smaller, river boats and barges and heads north through the Verduran Forest and up both forks of the Sellen, eventually reaching the cities on not only Lake Encarthan, but all the way up north to the Lake of Mists and Veils. Along its many, winding routes, it thereby connects the nations of Brevoy, the Five Kings Mountains, Druma, Galt, Kyonin, Mendev, Molthune, Nirmathas, Numeria, the River Kingdoms, the Sarkoris Scar, and Ustalav.
Because of the incredible importance of trade along the Sellen and its tributaries, governments that border these rivers tend to invest in well-regulated harbors and towns where a certain level of safety can be expected. Maintenance of these locations is supplemented by the taxes and tolls levied on traders and travelers alike. This does not mean that banditry is absent from the Sellen. Far from it, smugglers, pirates, and other brigands are common along its less populated stretches. These threats have created a secondary industry of river pilots and mercenaries to guide and protect travelers, although it is an open secret that these individuals often turn to piracy once business slows.