Acheron

The Infinite Battlefield of Acheron is one of the outer planes that inhabits the negative energy zone. Its denizens tend to be evil-aligned and focused on battle or violence. The plane is made up of massive metal cubes that float freely in an airy void. Various warlords and lesser deities control massive armies that clash almost constantly on these cubes.
More information about this plane can be found in the 5th Edition Dungeon Master's Guide, page 66, or in the Forgotten Realms wiki: here.

The House of Iron

One of the cubes of this plane houses the palace of the Olcrid Schrios, the Iron Hand. As the Lord of Tyranny, Torture, and Pain, he lays claim to most of Acheron as his territory. His forces fight against the likes of other lesser deities and upstart warlords hoping to eventually unseat the prince of the realm.

The Den of Knives

Another location on this plane is the hideout of the deity Stiletto. Stiletto does not prefer open combat, so their forces are more subtle in their conflict with rivals on this plane. As such, the location of their lair is a very closely guarded secret that not even Schrios knows.

Type

Dimensional plane