Whoops... maybe I should pick a less obscure one next time. *shrug* Oh well... never mind. I'll reveal it...
The book I was thinking of was Witches Abroad. The witches "discover" something (a waterfall, IIRC?) - and the footnote then says that everyone else discovered it on an almost daily basis, of course, but they're not explorers so they don't count.
Go ahead and pick a new footnote, MrsWizzard.