Lord Zack's Planescape
The known planes of evil touched by law consist of the four mounts of Gehenna. These are four huge, volcanic mountains hanging in an apparently endless void. This plane is ruled mostly by the Yugoloths from Oinos, a large portion of which have moved to this plane. They guard the secrets of this place, that, and it’s general hostility have led to a deficit of exploration, so no other planes comprising Gehenna have yet been discovered. Some expeditions have set out into the void in flying vessels but they have variously either not returned, or not found anything.