The green car is a vehicle which moves along the groove cut into wall. It is parked on the lake floor and moves along the lake walls. The green car's grooves are numerous and branchy, leading to many different places:
- Lake wall radio: This must be visited in order to know which song must be set on radio in the Radio Tower to open the door to the Purple Building.
- Test tubes: This mix of liquids will make Klaymen back normal-sized in the Purple Lab.
- Cannon Monument: A plaque telling that the cannon was put there by Hoborg.
- Red roofed house: The longest groove takes Klaymen to Willie's bedroom, a remainder of Ottoborg's World.