I think I found a link to this over on Grognardia.
On page 18 of this PDF copy of an old wargaming fanzine is an article about designing a D&D campaign by Gary Gygax.
It's really interesting for a lot of reasons - historical for one, as a GM's set of design notes for another, and for being a lot less pontifical than Gary Gygax's writings for The Dragon.
Plus I'm totally going to steal bits from it for my own DF game's dungeon. No question about that!
Thanks to whoever held on to this old fanzine for years and then got it scanned.