River Caves are a wet underground network shaped by flowing water rather than clean excavation. Narrow rock passages open into larger chambers where channels and pools cut across the floor, forcing characters to move around the water or risk crossing it. Natural stone keeps the route irregular, and the constant change between tunnel and river edge makes the complex feel carved by erosion instead of planned by builders.

In Rise of the Runelords: Fortress of the Stone Giants, these caves extend the wilderness beneath and around Jorgenfist. A GM can use water to divide the party, hide creatures beyond bends and turn apparently simple crossings into vulnerable moments. The map also works as a mountain river cave, smuggler route or flooded underpass in another campaign, especially when the goal is to make underground travel feel different from a dry dungeon corridor.