The Dark World are just the same levels a few magnitudes more difficult.

To switch between Dark and Light World, you just have to press <kbd>X</kbd> on your gamepad or <kbd>Shift</kbd> on your keyboard in the level select screen (see an example on [Wikia][1]).


  [1]: http://supermeatboy.wikia.com/wiki/Chapter_1:_The_Forest?file=CH1lightworldmenu.png