This Achievement is for finding the secret area and Colin on
Mission 05 Stage 01 : Bamboo Garden
Play the stage as normal from beginning to end. Once you get to the end , don't collect the exit sign , but make your way all the way back to the top of the mountain. Colin (Boss from Mission 1) will be here waiting to do battle. The Achievement unlocks as soon as you finish speaking to Colin as you can see in my video as he kills me immediately.