I'm at it again on Amazing Stories!
This time, it's setting-focused. The plot is uncertain until partway through the first part of any story that would be written about the subject.
The Best Terrain - published today
Getting to pick the type of terrain means no ocean dumps. (That grumpy genie might send you there if you don't pick, though.)
The protagonist's decision-making process tells a lot of the story: not only where he or she ends up but also which other characters might appear. For example, I don't think the protagonist will befriend a harp seal in the midde of the Sahara. With so much possible, and so little of the story told before the big event (although the protagonist will have to do some all-weather preparation!), it's a prompt a hundred people can write a hundred different ways.