Before doing this you must have unlocked the 10 hidden eggs (you get an individual achievement for each one) and beaten the game. After you have done that load up Chapter 26, it has the wasp/fly thing in the preview picture, and follow the video below. It's very informative and it tells you where everything is and what to do. Credit to KillerSnowTiger for the great video. The level is nearly in complete darkness so good luck.
and yes there are checkpoints if you die don't worry.