Heliopolis

Heliopolis was a plane that across cosmologies was considered the home for a number of deities within the Pharaonic and Mulhorandi pantheons.

Cosmography
Under the Great Wheel model, Heliopolis was said to be a single divine realm that resided on Buxenus, the second layer of the plane of Arcadia. Jointly ruled by Ra, Isis, Osiris, and Horus (later Horus-Re after his Ra's death). While under the World Tree model, it was considered to be one of the Neutral Planes that were connected to the World Tree and the home of all members of the Mulhorandi pantheon.

Great Wheel
Under the Great Wheel cosmology, this realm was said to be an immense burning desert of bright sand that was laid out like a triangle, divided into three equally sized domains. It was touched at every corner by a scorching sun, which was guided across the sky by Ra's solar barge Manjet. This was in contrast to the rest of Arcadia, which received light from the Orb of Day and Night, though the time of day for both coincided. When the time for day to end came Ra's barge became a funeral barge, referred to as Mesketet, and briefly provided light to the realm of Osiris.

Whenever the sun faded in Heliopolis the temperature would drop dramatically. However, the overall temperature varied between the three domains that each deity governed. The domain of Ra was the hottest of three, the heat striking even indoors and in shadowed area. Fauna were almost never seen out during the day in his realm, due to the unbearable heat of the sun. The valley that Osiris presided over was the coolest of the three, even when standing beneath the sun. And the sloping domain of Isis between them was moderate in temperature. With its moderate temperature, this domain was where all wildlife and most plants were found, being spread over with thick grass and dotted with fig and palm trees.

Creatures that were known to inhabit Heliopolis included lions, camels, serpents, and scorpions.

World Tree
Much like the Great Wheel conception of the plane, the Heliopolis of the World Tree was said to predominantly be a great arid, desert realm where Horus-Re sailed a solar barge across the sky each day. A body of holy water known as the River Isis flowed through the desert, irrigating it and providing a source for all life in the plane. It was also home to oceanus dragons. The land along its banks were a fertile valley named Succor, covered in thick grasses and dotted in both figs and palm trees.

Further out beyond the rivers one could find all manner of monuments dotting the desert landscape &mdash; mausoleums, obelisks, pyramids, sphinxes, and temples. In the middle of the desert stood a mountain range, the sole source for the rocks used for the plane's monuments.

Great Wheel
Ra and Osiris were considered to be the dominant powers of Heliopolis, while Isis and Horus held secondary realms. They shared the role of leader depending upon what pressing business they had to attend to. Horus wandered between all three realms, rather than having a realm of his own, at least up until his change in station.

The Great Wheel model also claimed Heliopolis to once be home to the Pharaonic deities Set, Geb, and Nut. The former was banished for his transgressions, while the latter two chose to leave after the god Shu forbade their marriage.
 * Thekele-Re, the First Realm of Heliopolis, was the domain of Ra. Following the death of Ra's Mulhorandi incarnation Re, his son Horus received both his powers and divine realm, taking up the new name of Horus-Re.
 * Gizekhtet, the Second Realm of Heliopolis, was the domain of Isis.
 * Memphiria, the Third Realm of Heliopolis, was the domain of Osiris.

World Tree
The only Mulhorandi god that was not said to reside on the plane was Sebek, who spent much of his time lairing on Toril and in the realm of Set. And beyond the members of the Mulhorandi pantheon, the goddess Tiamat was said to sometimes reside on this plane, maintaining a portal to the plane of Dragon Eyrie.
 * Amun-thys, the divine realm of Nephthys. Located in an uncultivated part of the fertile valley, it was full of temples and tombs.
 * Ankhwugaht, the divine realm of Set, was the harshest region of the Heliopolis desert and the only one where Horus-Re's light did not shine.
 * The divine realm of Hathor was a single village within the valley of Succor.
 * The Caverns Under the Stars, the divine realm of Geb, was a great cave complex at the root of the mountains of Heliopolis.
 * Gizekhtet, the divine realm of Isis. It was a great city whose center the River Isis flowed through, making the land around the city the most fertile and lush in all of Heliopolis.
 * Memphiria, the divine realm of Osiris, was an immense necropolis in the desert reaches of Heliopolis.
 * Netaph, the divine realm of Anhur. It was situated between the arid desert and fertile valley.
 * Thebestys, the divine realm of Thoth, was a great city that stood in a marshy area along the river banks. Several smaller villages stood around it.
 * The skies of Heliopolis served as the divine realm of Horus-Re, though his petitioners lived on the ground in a city named Thekele-Re.
 * The goddess Bast had a small, unnamed divine realm in this plane, which was linked by a portal to her realm of Rapture in the plane of Brightwater.

Inhabitants
According to the Great Wheel model, the realm of Heliopolis was home to petitioners from all many worlds across the Prime Material plane. The World Tree model, being more Torilian-centric, was said to only host petitioners that were Mulhorandi in origin. These petitioners appeared as they did in life, but at their healthiest and most robust. Additionally, in both models the petitioners of Osiris wandered his realm as undead of good alignment, who were treated as no different from the living by the realm's other petitioners.

Beyond petitioners, one could find angels and lillends serving the good deities of the plane. And a diverse array of horrible creatures could be found in Set's plane of Ankhwugaht.

Rumors & Legends
Some legends claimed that the great serpent Apep was buried beneath the sands of Heliopolis.