The Necromanteion is a black citadel, carved out of ice, and lies on Carceri's deepest Layer, Agathys. It is the Realm of the Nerull, Oerth's Power of death, called the Reaper, the Foe of All Good, the Bringer of Darkness, and similar names. Petitioners here are frozen flush into the floors, walls, and ceilings of the Necromanteion, just as they are in the surrounding ice.
The deserted entrance to the Necromanteion leads quickly to a wide hall called the Hidden Temple, which crawls with undead of all types. The pallid, green glow of gibbering ghoul-light lanterns illuminates the area. Hundreds of onyx altars are evenly spaced around the hall, and demonic clerics constantly chant stanzas of a ghastly necromantic ritual. Besides chanting, the evil priests spend endless hours attending grotesque experiments on necrotic flesh piled on other altars. Nerull's throne stands at the center of the Hidden Temple.
Woe betide the character who disturbs Nerull, a rust-red skeleton wearing a dull black cloak. Always clutched in Nerull's skeletal hands is his sablewood staff. Lifecutter, which projects a scythelike blade of scarlet force that has the power to slay any creature.
The Hidden Temple has several satellite chambers. Some hold food and quarters for the Reaper's clerics, others have cells for living captives destined to be strapped onto an onyx altar (or become food for a hungry priest), and in some are special vaults where the relics of Nerull's faith are sealed away. Finally, small tunnels lead deeper into the ice of the layer, supposedly connecting to vaults of horror so ghastly that even the priests shy from exploring their depths. Otherworldly wailing and whispers rise up from the depths.