The Virtual Limbo was only seen once in Frontier. It is also mentioned in Exploration. It is a null space between Lyoko and the real world in the recesses of the Supercomputer's memory. It exists within the supercomputer's memory, which Aelita was linked to. Normally, it's not seen unless the virtualization or devirtualization phase malfunctions via data capturing errors that block the system.
It's apparently tied into the same sector of memory that the scanners use, since the Lyoko Warriors are sent through this area on their way to Lyoko, and were unable to use the scanners while Jeremie was stuck there. They were however, able to get together enough memory for one scanner, meaning that the scanners aren't hardcoded to particular memory sectors.
Upon his arrival, Jeremie was able to speak to Aelita through her link to the supercomputer's memory. Through the link, Jeremie was able to tell the others how to free him. After traveling to all four Sectors and collecting the scanner memory from all four way towers, Aelita was able to travel into the limbo and free him. During that time, their minds were melded, allowing them to sense the others feelings.
Odd, Ulrich, and Yumi were all trapped in limbo in Exploration due to the lack of the specific materization code needed to return from Sector Five. This caused a data capturing error. Fortunately, they were saved after Aelita found the right code in the Sector Five Interface, and Jeremie used it to bring them back to Earth.
Users stuck in Limbo are on the verge of being deleted by the Supercomputer. The quantum computer confuses the person as an "out-dated" file according to Aelita. The only Lyoko Warrior who has never been in the limbo is William. The only recovery methods of exiting the User from the Limbo is to retrieve all the Scanner Memory from the Passage Towers, or by entering the correct materialization program.
|Ice Sector | Desert Sector | Forest Sector | Mountain Sector | Carthage|
|Ice Replika | Desert Replika | Forest Replika | Mountain Replika | Volcano Replika | Carthage Replika|
|Other Virtual Worlds|
|Digital Sea | Cortex | Virtual Limbo | Simulation Bubble|
|Dormitory Building | Administrative Building | Cafeteria | Gym | Track | Park | Hermitage | Science Building | Playground | Garden Shed | Infirmary | Boiler Room|
|Union Base | New Mexico Research Facility | Space Station | Jungle Research Facility|
|Renault Auto Factory|
|Factory Floor | Factory Lift | Lab | Scanner Room | Supercomputer Room | Assembly Room | Security Center|
|Kadic Academy | The Sewer | The Factory | Ishiyama residence | The Pool|