The Ghost Zone is a fictional dimension from the Nickelodeon animated television series Danny Phantom. Highlighted in season 3, the very fabric of the Ghost Zone co-exists with the physical world; their mutual and dual existences is interlinked; they are the proverbial 'flip-side-of-the-coin' to each other. The 'Ghost Zone' is a dimension composed of variations of ectoplasm where 'ghosts' exist and through naturally occurring portals can cross-over into the human world, hoping to make a scene or take over mankind.
Danny Phantom's life was actually permanently changed by a portal into the Ghost Zone when he was involved in an accident in his parent's basement laboratory. Danny's parents, Jack and Maddie Fenton, constructed an artificial Ghost Portal, a gateway into the Ghost Zone, which Danny accidentally activated while standing inside, fusing his DNA with ectoplasm and making him half ghost.
The Ghost Zone is the first level of Nicktoons Unite!. After you arrive in Amity Park, Vlad sends you to the Ghost Zone where you end up in the Ghost Prison. You have to find your way out of the Ghost Prison and fight Walker at the end.