How do you move the boulder on Mythology Island?

Only Hercules has the strength to move the boulders at the throne rooms of Hades and Poseidon. And Herc will not help you until after Zeus has stolen the Sacred Items from you, in his bid to rule Poptropica.

To reach the throne rooms with Hercules, you need the Touchscreem Mirror from Aphrodite's test (on the beach in Poseidon's realm).