In the second level of the island, after the level where you get there, and there' s that big base with the gun guy, there's that next level, where everyone is attacking. Just follow:
Get on the island. Go through the first level. When you get up the ladder, go up, kill that Gonado, jump over that cliff space, jump over the windowsill, waster whoever's inside. If you see, in the cavern, a red explosive barrel, shoot it. You'll find a hidden cave, and there is a giant rock with the treasure chest on top, inside is the Sphinx Treasure. There you go.

u use those jewels in a beerstein mug which is hidden in the village. U have 2 break the shelf which is blocking the way.