The Vein is an enormous river that passes under the [Frostquill Mountains] connecting the northern and southern halves of the continent. It is by far the safest, cheapest means of travel, and is the route of choice for merchants travelling long distances.
A large section of the river runs underground through a series of caverns within the Frostquills. Although these caverns remain largely unexplored, they are not generally considered a threat to vessels on the Vein, especially since the Nightholme guard has devoted resources to patrolling the entire length that runs underground.
As the river approaches Nightholme, travelers will notice a series of portcullises that can be lowered to stop travel through the city. These gates have not been lowered in 25 years, since the time of the last [Gossamer Moon].