The realm of the dead is as the word says, dead, but many have picked up ancient Greek myths or even older pagan mysteries and made them beliefs such as Purgatory, Limbo and Hades. It comes from the worship of the dead or ancestor worship which involve addressing prayers or offerings to the spirits of the dead. It existed among the ancient Greeks, other ancient people. The practice of worship for the dead and praying to them, or making prayer or offerings on behalf of the dead to contribute to their afterlife purification is not scriptural and in fact is forbidden in the Bible.
10 There shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch.11 Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer.12 For all that do these things are an abomination unto the Lord: and because of these abominations the Lord thy God doth drive them out from before thee.
Purgatory is the belief that presupposes that the dead can be assisted between death and their entry into their final abode. Purgatory is given as a way that no matter how sinful or unbelieving, when you die, you go to Purgatory and get things sorted out and finally get to heaven, so no acceptance of Christ is needed, you can buy your way in. In ancient Egypt in the worship of the dead, substantially the same doctrine of purgatory was taught as today and its priests created grand funerals and masses for the dead, along with celebration of prayer and other services for the dead.
Now Limbo as a belief seems to presuppose that the dead are held in the Greek myth of the underworld (Hades) and came to be associated mainly with Limbo of Infants, where the unbaptized who die in infancy, too young to have committed personal sins.
The problem of picking up these ideas from Greek mythology is because of the Greek words used in translating from the Hebrew text has become confused with Greek myths. Christians picked up these false ideas and beliefs of immortality of the soul, or that a part of, or essence of, or spirit being of an individual being held in the underworld, from Greek mythology. This is at odds and in contrast to the scriptural teaching that the dead go to the grave and know nothing and at the end, a eternal oblivion of the wicked and a eternal life for the saints.
The Greeks had come up with myths that all the dead dwell below the earth in the realm of Hadēs and Persephonē, good and bad alike, and were held in a dark existance. The Greek god Hades was the king of the underworld, a place where souls live after death. The Greek god Hermes, the messenger of the gods, would take the dead soul of a person to the underworld. Hermes would leave the soul on the banks of the River Styx, the river between life and death. Charon, also known as the ferry-man, would take the soul across the river to Hades, if the soul had gold: Upon burial, the family of the dead soul would put coins under the deceased's tongue. Once crossed, the soul would be judged by Aeacus, Rhadamanthus and King Minos. The soul would be sent to Elysium, Tartarus, Asphodel Fields, or the Fields of Punishment. The Greeks picked up many ideas from the Egyptian beliefs of the Book of the Dead and developed them further in how the dead continue to exist, and of reincarnation and even transmigration of souls. These ideas are particularly associated with the pagan Greek Religious Mysteries or Eleusinian mysteries , where initiation in this life into its ‘mysteries’ are the prerequisites for getting to paradise in the next life.
So you see where the Greek words used came loaded with ideas not in line with the original Hebrew, or what Scripture teaches, but since at the time, Greek was used as basically English is used today to communicate between people across the world, it was translated into these Greek words, and we have to go back to what the original Hebrew scribes words they wrote to understand their meaning.
Hades was the Greek work used in some places for the Hebrew term, Sheol or grave as "the place of the dead". Thus, it is used in reference to both the righteous and the wicked, since both wind up there eventually.
Gehenna refers to the "Valley of Hinnon", which was a place outside of Jerusalem where people burned their garbage and thus there was always a fire burning there. Bodies of those deemed to have died in sin without hope of salvation were thrown there to be destroyed. Gehenna is used in the New Testament as a metaphor for the final place of punishment for the wicked after the resurrection.
Tartaro occurs only once in the New Testament in II Peter 2:4, and basically means the abyss or oblivion. Also the Hebrew word Abaddon, meaning to perish or "destruction", is sometimes used and basically means the same as the abyss or oblivion.
As you can see, Hades is the Greek word used for the Hebrew word Sheol in Greek translations of the Hebrew Bible. While earlier translations most often translated Hades as "hell", as does the King James Version, modern translations use the transliteration "Hades", or render the word as allusions "to the grave", "among the dead", "place of the dead" and many other like statements in other verses. In Latin, Hades began to incorrectly be translated as Purgatorium or Purgatory in English, around 1200 A.D., but no modern English translations put Hades as Purgatory.Modern translations, however, no longer translate Sheol as "Hell" at all, instead rendering it "the grave," "the pit," or "death."
So if one really looks at the true meaning of the words, it becomes clear, Purgatory, Limbo, and Hades are Greek Myths which got mixed in the translation, and the dead are in the grave, knowing nothing and quite dead, literally.