Realms are different planes of existence in all of creation. Most of the realms were created by God. The realm primarily seen is the The Universe. The other realms created by him consist of Heaven, Purgatory, and Hell in that order which were created by God. However, Avalon and the Empty's creator is unknown.
The realm of the angels and souls of humans deemed worthy to enter into its gates. Guarded by the angels of God and led by the archangels.
A realm where Reapers can send souls, rather than Hell or Heaven. Angels and demons reside there after they got killed and exist there in eternal slumber. According to the Reaper Billie, once a soul is sent to The Empty, it can't be resurrected as God has no control over this realm.
The only way to leave is if the Cosmic Entity, residing there awakens and decides to send the person back in order to return to its slumber. The Entity can effortlessly resurrect even someone whose body had been burned and salted like Castiel who was the only known person to awake and escape the realm.
- Of the realms seen Hell is the only one seen in a dark demeanor reflecting its purpose as a place of torture.
- Earth and Purgatory are the only known realms where everything is tangible and existent. Avalon is unseen and Heaven and Hell are mostly memory reflections or illusions of torture and pain.
- Dean Winchester is the only known being to have been to all realms of existence (except The Empty), while Sam, Castiel and Bobby have been to all but Avalon.
- Castiel has been the only being so far, to been shown to have come back from The Empty after he demanded to the Cosmic Entity to release him.
- Heaven and Purgatory are the oldest of the realms, followed by either or Earth and then Hell. Paradise existed, soon chaos rolled in, and then when evil came Damnation was created.
- The Earth realm has the most beings walk though it; Purgatory and Hell being second with angels, monsters, demons, humans, and reapers/Horsemen. Heaven has the least with the least angels, humans, and Horsemen.
- It is currently unknown if there is one God who created the alternate realities, or if there are also other versions of God, or if they were created by him at all.
- Given that the Entity of The Empty has stated that not even God has power there, it is unclear how God managed to resurrect Castiel so many times.