Darkness

The dark river water seemed as black as ink, perfectly melding with the rest of the always-dark Underdark.

Although the other rivers in the Underdark also tended to be quite dark, there would usually be some bioluminescent aquatic plants that would serve to brighten the area to some extent.

But here, everything seemed to have been swallowed up.

The true power of Darksight could only be displayed in this kind of location.

Marvin was like a fish in water as they travelled along the dark river. They were steering a small boat, following the current.

Jessica was a Fate Sorceress, so she could naturally adjust her perception and use various other methods see and otherwise know about her surroundings. But because of the unusual qualities of the Deep River, she definitely wasn't equal to Marvin here when it came to how well they could see.

At the same time, they had a sort of unfathomable feeling.