Underground

As well as under the floorboards, some interesting things can be seen underground.

As the townspeople mine down to rescue Bart, you can see a dinosaur skeleton, pirate's treasure chest (and his skull), and an alien spaceship. The skeleton inside resembles the standard Simpsons alien design like Kang/Kodos.

When the Simpsons fly to Australia, the camera pans down through the Earth. First we see a set of coffins, in one of which the person was buried alive and tried to escape, then some dinosaurs in coffins.

At the centre of the Earth, the Indian god Vishnu is operating some controls. As we move back to the surface under Australia, remains of the Skylab space station can be seen (debris from its re-entry in 1979 was scattered across Western Australia).

In the future, Ms. Hoover reveals that Martin Prince had perished in a science fair explosion. We then pan down, passing a skeleton torso, with one leg above him, then a treasure chest, then the skeleton's other leg.