Go to the 'Rest Area' inside the Plantation level and go to the bottom where the water is located. Reach the 'Inner Wall' outside area by moving left through the opening in the wall. Booster 2.0 is needed for this location. Keep moving ahead until you reach a door at the bottom left with a wall between it. Go under the wall and boost up until you reach the door which will take you to a 'Secret Grave' with a large 'Prinny' statue at the center. When you examine the sparkling object you will get the 'Prinny Cap'.
Added by: Sanzano Apr 19th 2012, ID#340