Rylayeh is a ten-level limit-removing PWAD for Doom II, created by Jeffrey Graham (psyren) and released in March 2006. The episode is inspired by the Cthulhu Mythos and employs new textures, graphics and music to create a unique atmosphere representative of the Lovecraftian horror genre. The levels are based on the fictional city of R'lyeh. The story follows the player battle against Hell, now entering into a new dimension where ageless and formless enemies lie, corrupting and spreading their influence in their wake. The player must travel to the city of these demons and defeat them.
In 2018, it was included into the Top 25 Missed Cacowards feature.