The Underworld is roughly the same size as the Human world, but with a much larger landmass, as there are no oceans just lakes. The sky was originally purple during both the day and night, but the current Four Great Satans adjusted the flow of time to match it in the human world for the sake of the reincarnated Devils. They reproduced an artificial moon using Demonic Powers and made the night's darkness the same with the human world.
The Underworld was originally split into two regions: The Devils' Region and the Fallen Angels' Region, which ended in Volume 4 after the creation of the peace treaty between the leaders of the Three Factions.
The current Capital of the Satan territory previously ruled by Sirzechs Lucifer and now being ruled by Ajuka Beelzebub. It has one of the most advanced hospitals, which is named Serafall Memorial Hospital.
The original Capital of the Satan territory ruled by the original Lucifer.
A large city that is located in the Agares Territory which is being maintained by the servants of the current Beelzebub. It has a distinctive feature in which it appears to be a large floating island suspended in the sky. A popular tourist resort, it is also the place that controls the flow of the air in the Underworld. The Agreas is a place that has the technology of the Original Satans and contains the essential crystals of the highest quality that is used to create both the Evil Pieces and Brave Saints. In Volume 17, Agreas was taken by Qlippoth. It was finally located by the Vali Team in Volume 20, where Qlippoth had been using the city to both wake Trihexa and create mass-produced Boosted Gear Scale Mails. By the time of Volume 21, it has been recovered and returned to its original location.
An agricultural town located in the Agares Territory which is said to have the best agricultural products in the Underworld. Sona Sitri's Rating Game school is being built here.
The Gremory Clan has a territory that is about the same area of Honshu in Japan. A very rich territory with developed industry. Located within the territory is the Gremory Palace, the home and main building of the Gremory Clan Head.
The Dragon mountain is also connected to and a part of the territory of the Gremory Clan. It was given and taken under the care of Tannin alongside his many and various dragons that Tannin took from the Human world. The reason why Tannin took this place was to obtain a certain fruit called Dragon apples in order for his other kin to survive. It was also here where Issei Hyoudou trained himself to enhance his dragon powers and Crom Cruach also lives here due to Tannin taking him under his care.
Realm of the DeadEdit
Also known as the Realm of Hades in Greek mythology and Depths of Hell. The place where Hades the God of the dead and the Grim Reapers reside. Located in the lower strata of the Underworld and the place where the souls of the dead are sorted and is also close to Cocytus. The realm of the dead is of the Olympus World; the God from the Greek-faction Hades is in control of it. It isn't as big as the Underworld and as it's the World of the dead, it is a wasteland that no living creature can live in. It also has an ancient Greek shrine as it appears into the depths. It is the place where the Grim Reapers of this World live and where the castle of Hades is located. There is a part in it that is something that looks like a ritual area. Ornaments such as gold are used for the interior and it's so gorgeous that it doesn’t suit being in the Underworld. There is a carving on the wall of the trinity Gods of Olympus – Zeus, Poseidon and Hades and it is carved to stand out. It's also where Vali's great grandmother Lilith is being held captive by Hades.
Purgatory was prepared for the deceased with special circumstances and to purify the spirits and souls who have died. It also the place were those who have died have are judged on if they are going to Heaven or Hell. It was also connected to one of the doors of Heaven like the Third Heaven. This is the place where Cao Cao was able to enter the Third Heaven.
The edge of the Underworld, is the place that it was speculative about the afterlife condition of those who die in original sin without being assigned to the Hell of the Damned and also the burning place. It is also connected to one of the doors of Heaven.
It’s the floor which is one floor above the deepest floor in Hell. It’s said to be the place where those who have evil minds, wicked souls, evil spirits who have committed sins get sent to and punished.
Also known as the Ice Hell, is the deepest part of the Underworld that is connected to the Realm of the Dead. It acts as a prison for powerful and dangerous figures such as Samael and Kokabiel. It is also serves as a home to many rare and dangerous creatures such as the Pale Horse. It’s for those who committed the gravest sins or those who perpetrated betrayals were eternally bound in the cruellest depths of Hell.
An RPG game created by Azazel as a joint project with Ajuka, Sirzechs, and the technicians of the Devil's side. The game uses the Devil's technology the Game Field, to provide an adventure-type experience. It’s an open-field RPG where within the massive field, there are things such as villages, caves, towers, and one becomes a player, who ventures through the area while slaying monsters. It’s an RPG game which can be experienced in first-person, where a person who plays the "Hero" can go on an adventure with their comrades and defeat the evil Dragon King! Participants who play as the hero's comrades can pick from a variety of roles such as Knight, Wizard, Priestess, or Clown, or play as a companion to the Hero and his comrades. A person can also play as an NPC such as a Villager or Blacksmith.
The game is still in development and a member of Grigori is overseeing the project after Azazel was expelled from the project. The game is developed for humans with special abilities who want to fight against mystical beings.
A smartphone game created by Ajuka, to use as a training ground for Rias’ team and Issei’s team.
- The current capital of the Satan territory, Lilith, is a reference to the female demon Lilith from Christian and Hebrew beliefs, mother of monsters.
- Seemingly named for Lucifer's wife, Rizevim's mother.
- There is a hamburger restaurant chain in the Underworld named Akuma-naldo.
- Malebolge means "evil ditches" and is the name of the eighth circle of Hell in Dante Alighieri's Inferno, part of the Divine Comedy.
- Azazel Quest was named by Azazel himself.
- The Underworld has many unique car models such as a sports car with an exquisite streamlined body constructed from mythril silver, uses demonic energy to run, and reaches 320km per hour (as fast as the Shinkansen); an ordinary sedan that is actually an iron golem that operates as a car; a ghost car possessed by a guardian spirit; a gigantic car that can fit all members of Team [DxD].
- The capital of Lucifaad has a stadium called Lucifer Stadium for the Azazel Cup in honor of Vali Lucifer.