OK I'm at the entrance of the temple where the mythical Sphynx was and there's a floating lock in the entrance. I see a pile of sand there but I can't do anything with it. How do I get in?

Use the Lich's Staff that you acquired from Skull Castle on the Lock...it should disappear and allow you entrance into the Temple of Isis. The lever to open the dungeon door is on the southern middle wall. Hope this helps.