The Ullen River (known by locals as the Dark River), originates from the farthest south of the Footprint Lakes(Twin Serpent Lakes). The River flows west past Riverside Province into the jungle, then turns decidedly south parallel to the Henge of Denravi, and ends at the marshes of Tangle Root. It is called the Dark River not just for the darkness of the passage through the cliffs but also for a perceived darkness that shrouds this river.
Old Joness says it's cast by something "unseen."
- Note: The White Mantle call their gods the Unseen ones. This might be a connection seeing as Saul D'Alessio supposedly stumbled upon their city in the jungle.
- The hidden Mursaat city is possibly Rata Sum (Rata Sum is an anagram of Mursaat), the city which the Asura found abandoned after being forced to the surface. It is possible that Rata Sum was once populated by Mursaat. However, the city itself is still located quite far from the Ullen River, making it unlikely that its shadow is what is darkening the river.