You need the pomegranates from the tree in the Garden of the Sphinx. Place them on the altar to enter the realm of Hades.
You need to offer the golden apple on the altar in the Hades temple on Mythology Island. This item can be found in a tree on the far left side of the Underworld.
To convince Hercules to leave on Mythology Island, you need to have the golden apple from Hades's tree. Offer it to Hercules as a gift and he will leave in search of more apples like it.
you need a pomegranate from above the sphinx
Hades crown and Poseidon's trident
Offer the starfish from the Poseidon statue in the Museum.
The Temple of Hades is in the Grove of Temples. You will need the Pomegranates from the tree in the Garden of the Sphinx (far left of the island). Place them on the altar and go down into the abyss, and cross the River Styx to find Cerberus and the Hades Throne Room.
Go right from the temple of Hades. To enter Poseidon's realm, you need the starfish from his statue in the museum.
It is to the far right, past the temple of Hades. To enter his realm, you need the starfish from the statue of Poseidon in the museum.
There is exactly one drachma. Get it from the worker in the underworld (Hades temple) for cleaning the graffiti. You will need it when you climb Mount Olympus.
you get a pomagranet from the garden of the sphinx and place it on Hade's alter at his palace. The alter is by the door. The door will then open.
Once you have the quest from Zeus, you can go right into the Grove of Temples: those of Hades and Poseidon. (You need the starfish from his statue in the museum.)
To move the boulder on Mythology Island, you need to obtain the Golden Apple from Hades in the Underworld. Offer the Golden Apple to Atlas, who will then help you move the boulder so you can access the entrance to the Underworld.