The Glimmersea Below the Sea of Fallen Stars lies a vast Underdark ocean called the Glimmersea, or sometimes the Sea of Starry Night. The Glimmersea lies 20 miles below the floor of the Sea of Fallen Stars. Its horizontal area overlaps that of the surface ocean for most of its extent, although the Glimmersea extends under some of the land surrounding the Sea of Fallen Stars, such as Altumbel and Aglarond. Similarly, certain portions of the Sea of Fallen Stars, such as the Easting Reach, have not arm of the Glimmersea beneath them. The Glimmersea's waters fill dozens of immense vaults. This waterway is noted for a number of spectacular ribbon-cascades that extend down into it from the cavern ceilings, thousands of feet overhead. In some of the Glimmersea's chambers, luminescent rocks in the ceiling glow like stars in a surface-world night, striking perfect reflections from the still waters of the sea's surface. This effect gives travelers the illusion of sailing amid a sea of stars. Despite its great beauty, few travelers cross the Glimmersea. Several powerful aboleth cities lurk within its starry depths, and in the shallows stand numerous kuo-toa and sahuagin outposts.
- Holy Mother Cauldron (Lowerdark)