What next after skull island?

I have finished the castle on skull island and I have gotten the treasure map from the pilot. I have underwater gear. And I have answered the sphinx's riddle. But I can't figure out where the treasure map is talking about (I have been everywhere underwater) and there is still a lock on the entrance to the temple of isis. There is some sand in front, which must play a role, but I don't know what to do with it. I am stuck roaming the earth aimlessly. Help please!

Thanks

Mac

[Sazerac]

Okay, well, you're at the right place. The Anephas Shrine is next in line. Remember the Lich? If you talked to him all the way through, he said after he accidentally "ashed" Anephas, he fled the Shrine and sealed the door with the staff. Got the staff? Unseal the door with it.

You won't be able to find the treasure until after you get to the "Lost Sea" area. Of course, if you're into a bit of tree-surfing such as I did....you can climb the walls at Brimloch, hop onto the trees, and cruise around the southern border until you get to the Lost Sea. (BTW, the treasure is nothing special, unfortunately...but it does mark the spot for Collasium (although it's the wrong entrance). The clue on the treasure map is far more beneficial for being able to find Collasium.

As I've said (tongue-in-cheek) before, the only use of the "useful" Pile of Sand is to bury the "useful" Rat Skull in it that you've been carrying around since the Crypt. (In other words, ignore it; it's one of those useless targetable items that at one time I imagine DW Bradley et al were thinking about doing something with and then just forgot about it.)

Hope this helps!

-Sazerac