The Cavern of the Rainbow Mosses was a the region of the Great Underground Empire known as the Cavern of Doom. The enormous cavity is easily a mile across, filled with rock formations of every imaginable shape. The ceiling, far above, is covered with with layer upon layer of phosphorescent mosses, glowing with every color of the rainbow.

In was to this cavern where Logrumethar, having been cursed by Grawl into the form of a hideous beast known as Grum, was exiled. Anyone who gazed upon him was instantly turned to stone. Thus when this region of the empire was reopened at the beginning of the tenth century by Syovar the Strong, all the exploreres who had entered were turned to stone. Hundreds of life-sized stone statues dotted the cavern. While the curse did not force Logrumethar to remain in the cavern, it was on his own freewill so that no one would be forced to behold his uglinees and be turned to stone. Once Bivotar and Juranda freed Logrumethar from the curse, Syovar the Strong restored all of the stoned people to their original condition and magical returned them to his Castle of Zork.