Atlantis. But Indy would be lame underwater, so the big climax would have to be it rising from the sea (then I guess crumbling).
Indiana Jones and the Search for the OOT
The bad guy should be interested in the object for art/ history/ the chase/ or collector reasons, rather than for what it can do.
Right, I used the term 'end-of-the-wlrd' loosely, but yes, I feel there needs to be more at stake if the bad guy gets the MacGuffin other than just getting it first.