I don't think there is a really clear description in scripture but, there's enough to know we don't want to be assigned there.
The only "thing" that always existed is God. Everything else is created.
Mat 25:41 “Then He will also say to those on the left hand, ‘Depart from Me, you cursed, into the everlasting fire prepared for the devil and his angels:
Everyone who does not inherit the kingdom of God.
1Co 6:9-10 Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God.
Those who do not show mercy. (Mat 25:41-43)
They chose the path of death rather than the path of life.
Those who do the works of the flesh.
Gal 5:19-21 Now the works of the flesh are evident, which are: adultery, fornication, uncleanness, lewdness, idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies, envy, murders, drunkenness, revelries, and the like; of which I tell you beforehand, just as I also told you in time past, that those who practice such things will not inherit the kingdom of God.
People go there because they choose their own way over God's way.