Mountain Sector

The Mountains in Season 1.

The Mountains in Season 2-4.

The Mountains are a sector of Lyoko. They are an area covered with mountains and craters that float over the Digital Void, which is heavily obscured by clouds. Very narrow paths connect the mountains to one another, and it is the only sector with moving platforms, like in real video games. The Mountains are primarily inhabited by very small creatures, such as Blocks and Hornets. Larger monsters like Crabs would probably fall off the edges, even though they appeared in the later seasons, due to the improvement in sector graphics and larger platforms to hold larger monsters, like Megatanks.
The Mountain's towers are usually out in the open, not hidden, like in the Ice Barrier. There is also a little vegetation here; trees can be seen across the landscape, although they are few and far between. The entire sector is covered in a grey mist, making faraway objects difficult to see. The Mountains are the most irregular sector. The actual landforms float all about, so sometimes jumping off a cliff will land you on another cliff.
This Sector has mountains that are holo carts which have paths that lead into them; inside them are large centers which where only shown in A Bad Turn. In Double Trouble, The Scyphozoa possessed Aelita and she destroyed the Mountains, but the sector was recreated in between William Returns and Double Take, and reappeared in Crash Course.