Outer Hells

The Outer Hells are one of the known layers of Hell in the world of Dota 2.

Description
Little is known about the Outer Hells, besides it being the home of the golem demons summoned by Warlock's. Warlock mentions the Outer Hells from where he summons his demons as “dark eternities” which implies its dark and eternal properties.

As a place of the gnashing of teeth, one can hear a great wail of suffering and anger when accessing Hell, a horrible sound perhaps produced by the damned.

Demons
is a demon spirit from the Outer Hells. Demnok summoned it into his Dreadwood staff, capturing it and binding it to his service.
 * The golemic demon is one of the many lesser Demons he has mastery over, as opposed to the “true devils” he has no mastery over, implying the inferiority of the Outer Hells and its own demons to the greater hells.
 * When attacking their master's enemies, these demons will curse their adversaries by wishing them an existence in the “demon realm” as enslaved souls, like these fiends.

Heroes
is familiar with the demon slave of Demnok, implying he knows this evil demon spirit of the Outer Hells.

Almost as an afterthought, summoned a demon spirit from the Outer Hells into his demonic Dreadwood staff.
 * His death animation has the same runic circle used by, implying he's banished to the Outer Hells upon death.
 * Possibly supporting this is Demnok claiming that his demons will bring him back from the abyss of death.

World
It's unknown if the Outer Hells are part of the Seven Hells or not. It's also unknown if they are related to the Lesser Hells.