Phantom Zone
In the Post-"Crisis" DC Universe, the Phantom Zone first appears after Superman returns from space with a Kryptonian artifact called the Eradicator. This device, created by his Kryptonian ancestor Kem-L, attempts to recreate Krypton on Earth, building the Fortress of Solitude; the extradimensional space in which the Eradicator finds the Kryptonian materials necessary is called the Phantom Zone. A Phantom Zone Projector is part of Superman's current Fortress. It has been used to access the Bottle City of Kandor and to trap villains such as the White Martians.