The Eiglophian Deep is the drowned remnant of a proto-Atlantean mountain range that once bridged the ancient continents of Hyperborea, Thuria, and Atlantis. In primordial epochs, before the first cataclysms shattered the world’s bones, this vast range was known as the Eiglophian Spine—a frozen, jagged barricade of cyclopean grandeur and immeasurable age. It stood as both highland and highway, a corridor of passage between realms now long sundered. The name Eiglophian survives like a ghost on both ends of this sunken bridge:

• In Elder Hyperborea, the Eiglophian Mountains form the frigid northern wall that looms over ice-bound plains.,

• In Hyboria, the same name is granted to the high peaks that crown the grim Realms of Cimmeria.,

Yet no map connects them, not in this age of Man. The lands have shifted, the seas have risen, and what was once a continuous spine of stone has been shattered and swallowed. The rift between them—the trench where the mountains once stood—is known in forbidden lore and fearful whispers as the Eiglophian Deep.

It is said to be haunted by the Deep Ones, that ancient amphibious race chronicled in the myth-cycles of Eldritch Scribes and dreamers plagued by visions not of this mundane world. Scholars of the Black Letters speak of ruined cities older than Atlantis entombed in the deep: basalt necropolises of inhuman kings, hatcheries for species that no longer dwell upon the land, and shrines to nameless gods that slumber still.

Seismic records and geomantic divinations suggest that the submerged range runs diagonally across the northern hemisphere, invisible now beneath leagues of cold water. Its drowned peaks form jagged ridges that snare dead currents and stir unnatural tides. Mariners do not cross it lightly—compasses reel, winds scream without cause, and dreams turn venomous. Some believe the Deep still links the sunken realms. That through these abyssal channels, the Deep Ones pass freely between north and south, silent mariners of a world that remembers, and waits—waits for the hour when the sea reclaims all, and the Eiglophian Spine shall rise once more to shadow the stars.