Heart of Darkling

There is a river that dips underground through a low-ceilinged cave before descending fairly gently under the grey hills to depths unknown. However, all it takes is a magic spell to lower the water level at the cave entrance to make this easily navigable by boat, as the river cave has a fairly high ceiling after the entrance…

Unlike my other ongoing megadungeon (the Tekumel Undercity maps), the Heart of Darkling series is being released for commercial use as the maps are drawn. The goal of the project is to produce 20 maps that are all tied together by a single underground river and lake.