This demo shows how to get all the nice powerups hidden behind a fan on level 11. These goodies are visible through a grate in the blue area, but the path to them passes through a fan near the level starting point. Also behind the grate, there is a secret door, protected by a force field. This door only opens from the side facing the grate. On the other side of the door is a switch that disables the force field and removes the fan! Once I trip this switch, I prop two doors open with markers, and take up a position near the fan. I then send a guided missile through the two open doors, through the grate, and into the "one way" secret door.