The Subterranean River is the lower section of the cave system known as Fedwyrr's Way, which runs through the mountains of northern Ehb. The Alpine Caverns lie above the river. The entrance is located along the road south from Jeriah's Trading Post, which lies in a small valley just beyond the exit of the Alpine Caverns. The Subterranean River exits into the Dark Forest.
The extensive caves and narrow, winding tunnels of the Subterranean River are best known for the veritable rainbow of crystalline growths present within, some of which are said to have a life of their own. Other creatures native to the caves include lectars, slargs, skicks, dark lungers, and spiked maws.
Adventurers engage a troop of Trog. A Trog Knight in the background can be seen wielding a Vengeful Hassat Scimitar.
The race known as the Trog also dwells within the lower tunnels. They were once far more widespread, but the 10th Legion's efforts to control their numbers significantly decreased their population. The surviving Trog are less aggressive, but still pose a serious threat if encountered in groups of more than two.
During the Seck Resurgence, the Krug invasion in the west and the battle at Fortress Kroth in the east drew soldiers out of the caverns, allowing the native Trogs to flourish in their absence. The future Lady Montbarron was forced to use these tunnels in her search for the stolen Staff of Stars.
A series of ruins deep within the caves
Near the center of the caves is an ancient ruin, littered with the bodies of slain Goblins. In order to navigate this dungeon, a series of pressure pads must be operated, activating staircases and doorways that lead down to a hidden treasure chamber deep below. Within this chamber was the eye of a Fury, which was brought to the Utraean Peninsula to complete a ritual found beneath the Utraean Circle in Hiroth.