NT3 idea?

I don't know a whole lot about ancient lost treasures in North America really, although in the first one they did end up searchin up in the Arctic... but what I think could make for a pretty awesome adventure and idea would be the Money Pit.

People have been trying for years to get deep enough into the Money Pit to find something, but somehow no matter what they do then end up getting foiled yet again, or they find another layer of stuff they have to break through that leads to another layer then to another layer etc etc. And when they think they're making some headway water fills it again and makes it impossible to get deeper into it. And nobody's figured out a way to stop the water.

Think about it, it'd involve pirates, treasure, a whole complicated series of contraptions to stop the water flow, maybe alternate exits and underground caves leading to it, and then once they figured it out it could be a huge cache of pirates' goods and spoils and treasures stored, with bits and pieces of all kinds of cultures of the past together and pirate culture. And if they wanted to set up a 4th one, they find a map leading to some other big huge historical lost treasure or mystery. I think it could totally work. I'd love to see it at least lol.

What are some other American legends/lost treasures? I saw the one about the Fountain of Youth, but I think that's too far-reaching into the world of fantasy for them to really use it since all the other movies have involved things that are primarily of historical significance and realistic relatively speaking.

EDIT: Oops.. I thought it was Oak Island NC for this... damnit there goes my thoughts that it'd have to be in the US. It's still North America though lol.