Level 11 is the eleventh level of the Main Tunnel of Run 3. The color has now changed and will stay like this until Level 20.
If you chose the Skater in the last cutscene, this is a good practice level for him. There isn't really much difficulty, as you just have to dodge holes. It might be a good idea to avoid the crumbling tiles as well.
If you chose the Runner, she is slower, allowing you to control her more effectively, but you will be unable to cruise across longer gaps like the Skater can.
Just be careful with jumping. Time each jump carefully, so as to avoid falling. Overall, this level shouldn't be impossible but may trouble beginners a little.