Level 20 is the twentieth level of the Main Tunnel.
Oh wow, is that a spiral level?
For this level, we highly recommend using the Skater as you can clear the level in two jumps. No, seriously. Two jumps.
But with the Runner, it's harder to do that as you have to move left in midair (changing gravity in midair). You can also do this: Jump, move right, and repeat.
And now the tunnel changes color. It's turning green.