Those cross-category quizzes can be a problem! If you do not get a definite response from an editor in one of the two relevant categories, there are a few possibilities that spring to my mind.
1. Write two quizzes, and focus one on man-made sites, one on natural wonders.
2. Decide which preponderates in your planned quiz, and write for that category. You might be able to give an appropriate slant to your questions so that they fit into the chosen category.
3. Consider placing it in General Knowledge - Thematic Fun. This is less satisfactory in terms of future players finding it as they browse, but might be a work-around.
And remember that the editors can re-categorise your quiz into a better spot if you don't get it quite right, or advise about any need to replace some qustions.
(Editor, Humanities, Literature and Books For Children)
That's all, folks!