Monument

http://commons.wikimedia.org/wiki/Category:Nude_female_on,_in,_or_next_to_tree

(You needn't bother actually going there; what amuses me is that someone saw a need for such a specific category to exist.)

Also, even granted the gender binary, why is there no Category:Nude_male_on,_in_or_next_to_tree ?  Maybe we need to upload lots of naked-bloke-in-a-tree pictures.