Cataracts

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I have no idea where this is, only that it looks cool. You don't want to be paddling your canoe into this shit, you bet.

I'd use it lke this:

1. Give the party information that the entrance to some underground cave complex or tomb or something, containing something they want, is behind a waterfall on the River of Certain Painful Death (or whichever river you prefer).
2. Provide them with landmarks to look for so that they'll know when they're in more or less the right place.
3. Allow them to struggle up-river through dense jungle for three or four weeks.
4. Eventually, when you're getting bored with their suffering, tell them that they've spotted the landmarks they're looking for and have them start casting about for the waterfall.
5. Show them the picture.
6. Have a digital camera handy to capture their expressions.

But then, I'm kind of a bastard.