Get on the roof of the building next to Stompy the Elephant. Jump on Stompy's back and grind her head to open the aquarium.

Alternately, enable the "Matrix mode" code as Jango Fett. Do an ollie and use the Jango Jump Jet twice. You will see the top of the aquarium. Land inside, save, and restart your PlayStation2. Stompy and his trainer will disappear and the aquarium door will be gone.

To enter the aquarium in two player mode, have one character play as Jengo Fett and enable the "Moon physics" code. Use the Jango Jump Jet until you are high enough to see the holes on the roof of the Aquarium. Then, try to fly towards the aquarium and drop in. Note: You will be stuck in there. This may be a good way to win the King Of The Hill game.