Age of Heroes 5e
Tartarus is a plane of ultimate Evil. It is one of the most accessible planes (to the living, that is), mainly because it is the midpoint of the River Styx, but also because the foundation of Mount of Olympus exists here.
The Realms of Tartarus are more commonly known collectively as the Glooms of Hades, because Hades makes his home here. This is an adequate description of evil at its worst. These are Realms without joy or emotion, without hope or peace, and without good will or intentions. Everything here is oppressively, unbearably, malignantly evil. To walk the Realms of Tartarus is to know ultimate despair and pain.
Tartarus is a gray land with gray skies in all of its Realms. All color is muted and dull and hard to distinguish from other colors. There is no sun, moon, stars or passing of seasons here. It is merely an unending state of dreaded waiting. There is no viable light source in Tartarus, but even so, a dullish red glow comes from somewhere. The dull, reddish-gray glow seems to come from everywhere and as such, there are no shadows here. However, if one encloses himself completely, the light can be shut out. There is no night or day and no weather or seasonal patterns in Tartarus as each layer is locked into its particular seasonal state.
The Evil of Tartarus is such that those who remain in its bounds for any length of time eventually become consumed by Evil. Mortals who have the misfortune of traveling through Tartarus risk being permanently trapped here, their existence fading over time until finally they are reduced to Shades.
The three Realms of Tartarus are fell regions, inhabited by monsters and great evil beasts. Unlike other Planes, the Realms of Tartarus, Hades and Oinos, are separate sub-planes, each one floating above the other. Portals between the upper two Realms are like flat windows through which one can leap or climb between the layers. These portals share common properties throughout each layer; portals found on the ground in one layer appear at a great height in the sky of the next lower layer. These portals are generally two way so that a traveler could leap from the upper-most layer to the next, or somehow fly up the portal of the lower layer to the higher one. The third Realm, Orthys, is completely cut off from the other two Realms.
Hades is named after its chief inhabitant, the Hellenic God Hades, who rules over the Dead with his sometimes wife Persephone in his Kingdom, The Land of the Dead.
The base of Mount Olympus can be found here in the Grove of Persephone and acts as a conduit straight through the Prime and into Olympus. The Grove of Persephone is surrounded by massive walls and gates and is filled with black willows and a single white laurel tree. The gates of Hades' Kingdom are massive structures of beaten bronze, dented by those powerful heroes or fell beasts who over the ages have sought to assault the Lord of the Underworld's fortress. At these gates sits the dread three-headed dog, Cerebrus, whose task is both to keep the living out of Hades and the Dead within. This is the only Realm of the Plane Tartarus through which the River Styx flows. Its mid-point on this Realm is the God Hades' fortress.
The Land of the Dead is as oppressively gray and evil as the Plane as a whole. Upon death, the souls of all men are brought here for judgment. Those who are deemed worthy are granted passage to Elysium; those who are not become Shades and are doomed to wander this Realm for all time. The Shades who roam here hate life above all things and will utterly destroy anything that is living if given a chance, even natives of the Lower Planes.
Oinos is ruled by Anthraxus, the Oinodaemon. It is a land of disease and rot and what life exists here is plagued by sickness. Mortals who find themselves here die of sickness and disease in a matter of days. Even the divine tread this realm with care.
Anthraxus' seat of power in Oinos is the mighty fortress Khin-Oin, better known as the Wasting Tower. This fortress is a colossal, massive keep of iron gray battlements, laced with crenellations and studded with towers and citadels. It towers nearly a mile in height and its dungeons burrow at least that deep into the gray rock. Its base is fifty miles square, though there are only two means of entrance (on the ground anyway). The Wasting Tower is continually wracked with internal power struggles and battles as other diseased greater Daemons seek to displace or weaken Anthraxus. Only the threat of an outside power or invader is sufficient to cause the Daemon masters to unite into a restless common front. When they do, they are unbeatable, for no other force or power has ever stormed or besieged Khin-Oin successfully.
The final Realm is also called Tartarus and is the eternal prison of Kronos. There are two portals into and out of this Realm. The first, and best known, exists in Hades, at the bottom of an abysmally deep chasm. This portal is tightly controlled the Lord of the Underworld. The second portal to and from the Realm of Tarterus can be found in Oinos. Anthrax knows about this portal, but does not set wards or protections about it. It is far from the Wasting Tower, but not far enough that the combined might of the Greater Daemons couldn't descend on it in force if need be. Anthraxus is not so keen on seeing Kronos released from his prison and would expend considerable resources to prevent such a thing from happening. In all the days since Kronos' imprisonment not a single being has passed through this portal.