|First appearance||Maiden Voyage|
|Also known as|| World Network|
|Terrain features||A network of tunnels built into what appears to be an upside down city, filled with pure blue liquid, with an occasional massive spherical/orbicular-shaped structure.|
| "Weird. It looks like an upside down city."
"If you ask me, all of these buildings are the network's inter-connective databases."
–Odd and Aelita in Episode 71, Maiden Voyage.
The Digital Sea (originally called the digital void) is a liquid sea that resides below all of the four main sector and is how the Lyoko program portrays the supercomputer's DOS or DOS's quantum computer equivalent. Another theory is that it portrays the trash folder. Aelita uses this to her advantage by dropping monsters into the Void using her Creativity. When a monster goes into the Void, a beautiful white column of light emenates from it. It is the most forbidden place in Lyoko due to the deletion it causes.
The Digital Sea is Lyoko's portrayal of the Internet, as the Internet was needed to create Lyoko, Lyoko shows the Internet as an actual sea to signify that all life needs water. Though it's actual properties are quite the opposite. If someone falls into the Digital Sea, their data is swept away in the "digital tide" and would be next to impossible to collect all their data back to re-create them. In some instances, X.A.N.A. used this to his advantage in Tidal Wave when he managed to flood Lyoko in order to protect his activated tower and to keep anyone else from entering Lyoko until the problem was fixed.
So far, there has been only one known incident of a person falling into the Digital Sea. Yumi fell into the Digital Void in Cruel Dilemma, but Jeremie was able to use the one-shot materialization program that Odd accidentally completed by dropping candy on Jeremie's keyboard to save Yumi and bring her back to Earth. It is unknown if Jeremie's current version of the materialization program would be capable of performing a similar rescue. Nevertheless, Team Lyoko continues to avoid falling into the Digital Sea at all costs.
Lyoko's digital sea is a small part of the overall digital sea. The 2 are connected by a kind of flood gate at the bottom of Lyoko. This floodgate was first shown at the end of season 3.
Most of the replicas, including the Cortex, have a sea and floodgate. The cortex's floodgate uses a different locking matrix. It's unknown if the non-canological Volcano Replika had one or not.
There are various Hubs in the Digital Sea that Aelita can guide the Skidbladnir into to teleport to other Hubs once Jeremie has entered the coordinates for them. They are often used when the Lyoko Warriors need quick transportation to different places, usually X.A.N.A.'s replicas of Lyoko. The digital sea also becomes red when a X.A.N.A. Monster or something unidentified (X.A.N.A. Destruction Program) enters it, it's surface does not become red though.
In season five , the entire digital sea glows reddish-orange instead of simply red whenever X.A.N.A.'s monsters are nearby.