Code Lyoko is a tv-serie seen on Jetix. It consists of 5 main characters who fight a kind of 'digital' force that wants to take over Earth. in every episode, the characters have to enter a digital, game-like world to prevent the enemy from harming their friends. Mostly, 2 or 3 characters enter that world, while one character with glasses operates a huge computer that monitors their progress. Another character, a girl with pink hair, is apparently trapped in the digital world and cannot get out. She always has the job to enter a tower in that world to 'undo' things that have happend. When she accomplishes her duty, a white light appears in the real world, while the character with glasses says 'Back to the past'.
The entire part mentioned above is the same in every episode, making it a bit repetitive and predictable in my opinion. I'm not saying you shouldn't watch it, but be warned; after a while it will be somewhat boring