Null Void

The Null Void is an alternate dimension created by the Galvan as a penal colony. It is filled with what look like never-ending floating rocks. Null Guardians are the guards of this prison dimension.

The Null Void is normally accessed by a Null Void Projector. Max is a known Null Void holder. He and his former partner, Phil, have owned one and trapped thousands of aliens in it while in their Plumber years. If a projector is broken and someone tries to use it, it self destructs immediately, similarily to a hand grenade, but with far greater force; Everything within a half mile radius, as referenced in Alien Force episode 6, Max Out. It is possible to release aliens within the realm.

Later in Alien Force, it is discovered that settlers live in the Null Void as well the descendants of criminals who made a living there for years.

In Alien Force, D'Void seized control over the Null Void and attempted to break through into the main dimension by means of a kormite powered-drill, but was defeated by Ben, Max, Helen, Pierce, Manny and some other aliens.

Trivia
The Null Void seemed to be a horrifying/unpopular place, for example:
 * Kevin was scared and horrified of going there.
 * Ben claiming that being in the Null Void is much worse than being in prison.
 * Argit hesitating to go there.
 * Vilgax had an eye twitch by just mentioning it, calling it accursed.
 * The Null Void is similar to the Phantom Zone, an intergalactic prison in the Superman universe that keeps dangerous criminals, such as General Zod.
 * For some reason, the Null Void is purple in the Original Series but red in Alien Force.
 * In Omniverse, the Null Void's appearance is a mix of the Original Series and Alien Force.
 * The Null Void is a setting in Ben 10: Galactic Racing.
 * The Null Void's name is a play on the term null and void, which means "having no effect".