ABANDONED. Children's Fantasy with a princess wearing a cone hat and a well on the cover

[Matt]

Hello everyone! I read this book in the early 90's. It is a children's fantasy book. The only thing I can remember is a part where a boy is climbing a tree and someone tells him not to look down or he will be stuck in the tree forever.
I also have less than a reliable memory about the book cover having a princess on the cover. The boy may have entered the fantasy world through a mirror?
Not a lot of information, I know. Any help would be greatly appreciated!

[Cupcakedoll]

This cover immediately leaped to mind, but I haven't actually read the book, and I may be misremembering the cover since it's hard to see the thumbnails!

[Nick]

This may be entirely unhelpful, but that sounds like something that could be in The Big Jump by Benjamin Elkin, but I haven't been able to confirm this

[Kris]

The Big Jump and Other Stories by Benjamin Elkin for Nick's suggestion.

[Lobstergirl, au gratin]

Matt, are you still looking for this or did you find it?

[Kris]

No response, moving to Abandoned folder.

Matt (OP) was last active on the site in June 2016.