Tytherion

Tytherion is a dominion in the Astral Sea plane in the World Axis cosmology, native to the Nentir Vale setting of Dungeons & Dragons. Called the Endless Night, it is the dark domain that Tiamat and Zehir share. No light can pierce its darkest depths, and both serpents and dragons haunt its otherworldly wilderness.

First touched upon in the 4e Manual of the Planes, it was further fleshed out in Secrets of the Astral Sea. It bears a passing resemblance to Gehenna and shares some of its features.

MotP Lore

A terrible realm of thirst, of darkness, of dragon-hunted deeps

Planar Traits:

• Type: Astral dominion.
• Size and Shape: Canyon maze about 100 miles across, 800 miles long, and up to 12 miles deep, surrounded by a belt of dry steppes 10 to 50 miles wide; bounded.
• Gravity: Normal.
• Mutability: Divinely mutable. (Deities control their own environs.)
• Alignment: Neutral Evil.
• Corruption: Attacks with the disease or poison keyword gain a +1 bonus to the attack roll. Healing powers restore only half as many hit points as normal.
• Necrotic Affinity: Attacks with the necrotic keyword gain a +1 bonus to the attack roll, and attacks with the radiant keyword deal half damage (ongoing radiant damage is not affected).

A vast maze of canyons shrouded in perpetual darkness, Tytherion is a monster-haunted wasteland where serpents lurk and dragons feed. Sinister temples brood over dizzying precipices, and grim fortresses dot the slopes and spires hidden in the lightless depths below. It is a plane of gloom, of despair, of disillusionment. Here voracious evil gathers its servants and its assets to itself, and hungers for yet more.

Astral travelers who breach Tytherion’s murky indigo color veil find their vessels aground in the dry steppes of the rimlands of a canyon in the heart of a great desert or arid savannah. Tytherion consists of a great canyon, or rather, a canyon complex. The canyon stretches for hundreds of miles. Scores of side canyons, hanging valleys, stony shelves, and mountainous mesas complicate its depths. In many places, canyons cut into other canyons, and the deepest lie a dozen miles or more below the surface.

As travelers descend lower and lower into this brooding black maze, they pass from the desert of the rimlands down through a steep belt of dry, dead brush, where black pines and vicious brambles cling to the slopes. Moving lower still, and the brushland gives way to barren rock, choking fumes, and ash—for in the lowest depths volcanic vents feed sluggish streams of cooling lava that wind through the canyon floors.

Tytherion has no sun, no moon, and no stars. Above its barren mesas a thick cowl of black clouds seethe, lost in the gloom that pervades the plane. The only light native to the plane comes from the evil glow of magma rivers in the lowest depths and the occasional flash of lightning in the black skies overhead. From time to time, violent thunderstorms scour the land, sending torrents of cold water cascading down into the canyons below. Most of the water evaporates by the time it reaches the bottom, turning into layers of steam and vapor that offer the dry brushland a small amount of moisture. How the dead trees and briars grew in the first place, none can say.

Powers of Tytherion

The deities who rule in Tytherion do not pay much attention to their benighted realm. Both Tiamat and Zehir are content to allow their servants—and the monsters native to this awful place—to struggle on as best they can, thereby proving their worth.

The steppes, deserts, and higher canyons of Tytherion are the domain of Zehir. Mortal spirits who displeased Zehir in life are transformed into tormented serpentine monsters. In their mindless anguish, they may yet prove useful by guarding his temples. Mortal spirits who pleased Zehir are rewarded with the opportunity to continue their service to the god of night in the afterlife as darksworn. They remain in their humanoid forms but are granted serpentine features—forked tongues, fangs, lidless eyes—as marks of Zehir’s favor. They serve as priests, acolytes, and temple guards who grovel and chant in the black temples Zehir orders to built in his own honor.

Tiamat rules in the lower canyons, haunting the volcanic depths of Tytherion. She claims comparatively few mortal spirits for her own. Those she chooses as her darksworn are left to their own devices in the fuming depths of the plane. The strongest and most clever make themselves into lordlings, ruling over their lessers in the brooding castles of the depths. With little required of them by their dragon goddess, many of these servants of Tiamat continue their former lives of avarice and amass hoards in the afterlife as well. They can be found pursuing their greedy schemes in places such as Sigil, Gloomwrought, Chernoggar, or even Hestavar. Those who fail to win a place for themselves in this heartless order are left to fend for themselves outside the citadel’s walls and become the playthings of the dragons who roam throughout Tiamat’s domain.

Tytherion is also home to a number of outcast devils. Chief among these is the archdevil Geryon, who once ruled Stygia, the fifth hell. The devils of Tytherion are a wretched lot. Some pursue schemes designed to regain the favor of Asmodeus, some continue in their proud rebellion and make empty boasts about wreaking revenge on their infernal rivals, and still others sell themselves as planar mercenaries. Doubtlessly, some of them are also only feigning their disfavor and are secretly serving Asmodeus in their “exile.”

Sites in Tytherion

In the dry steppes of the rimlands, ancient roadways zigzag down into the depths past the brooding ruins of zigguratlike temples. Outside the chasm’s rim, much of the plane seems devoid of level ground. Treacherous slopes of barren rock and scree constantly threaten travelers with the possibility of a fatal fall. Tytherion is warm and dry in its upper reaches, but its depths are hot as a furnace.

Amun-Atl: This massive stepped pyramid of black stone stands atop an island plateau and is the seat of Zehir’s power. Lesser temples and dark monasteries surround the central ziggurat, which is a city of darksworn acolytes and assassins devoted to their scaly god. Zehir resides in a vast, lightless maze beneath the ziggurat, but he rarely emerges from his den to acknowledge the devotion of his worshipers. His eyes are fixed on his plots against rival deities. Atlathessk, the Seneschal of Night, a yuan-ti exarch who governs in Zehir’s name, runs the domain. Atlathessk demands a steady supply of living mortals to slay upon Zehir’s altars, which means that the denizens of Amun-Atl often deal with githyanki slavers or launch raids of their own against mortal worlds.

Caverns of Fiery Splendor: Beneath the deepest pit of Tytherion lies a vast cavern complex of flowing magma rivers and stone ramparts. This sprawling, labyrinthine cavern system is the lair of Tiamat, the Queen of Dragons. The darksworn spirits of evil dragonborn, outcast devils who have sworn allegiance to Tiamat, dark angels, and all manner of draconic spawn fly, crawl, and slither through these vast caves, fawning on the Dragon Queen. Five great wyrms— white, black, green, blue, and red—serve as Tiamat’s consorts and guard her hoard, a collection of treasure that beggars the imagination. Within Tiamat’s lair stand a set of adamantine gates over 100 feet tall. Tiamat does not reveal what might lie beyond them and has never allowed them to be opened. Some sages speculate that mighty primordials were bound and imprisoned behind them long ago.

The Crawling Castle: A strong keep of iron walls and forbidding ramparts, the Crawling Castle roams the middle canyon level of Tytherion. It is called the Crawling Castle because it is carried upon hundreds of clawed iron legs. The castle is the citadel of the dark demigod Vulkur Vaal, also known as Vaal the Flayer. Vaal is a cambion warlord who cut a bloody path through the mortal world centuries ago before raising his sights to the abodes of the deities. He dabbles in the darkest sort of magic, seeking the power to make himself greater than any deity. The Castle itself is a mighty artifact that answers to Vaal’s will alone. Tormented souls swing from iron gibbets on its battlements, and mercenary devils watch over its iron gates.

Hopelorn: In a hanging vale filled with thorny forest stands the obsidian necropolis of Hopelorn, the stronghold of the lich-lord Melif and his cabal of undead mages. Sarcophagi glow dimly with an evil green phosphorescence in the necropolis, shedding a ghastly light over the vale. It’s rumored that Melif earned the wrath of the Raven Queen for his necromantic experiments and therefore withdrew to Tytherion. Horrible undead creations plague the vale of Hopelorn, and the darksworn have learned to give the place a wide berth lest they become the necromancer king’s next subject.

Yithomel: Within this forbidding citadel, a cabal of Tiamat’s most powerful darksworn spirits rules over a vast region of Tytherion’s middle level canyons. These are the Seven Kings of Yith, mortal monarchs who each devoted their lives to a truly draconic lust for wealth and splendor. Each of the kings competes fiercely to amass more wealth and influence over mortal affairs than the others, with each of them engaged in an endless game of one-upmanship. Dozens of maruts who are bound by centuries-old contracts to protect their gluttonous employers guard the fortress.

SotAS Lore

Secrets of the Astral Sea greatly expands on Tiamat's realm of Azharul, Zehir's realm of Samaragd, and the realm's border islands called The Scales.