How do you get in to the realm of Poseidon in Poptropica's Mythology Island?

I vaguely remember that you had to get the starfish (of seadollar, I forget since I finished Mythology Island when it first came out and haven't been on for a while :P) and go above Hades Temple with the rocks that were shot up with the gas.

Then, you place the starfish onto the thingy and it should open up for you, that's what I remember from doing it.