http://www.geocaching.com/seek/cache_details.asp?ID=17343

you can probably figure out the locale with an online map server. At
least, you can narrow it down to the street and probably make _the
educated guess_ once you're in the vicinity.

Once in the building, the entire process is clue-based. (GPS is no
help inside.) And there probably IS a unique stamp available in the
building, although not in the final piece of the puzzle.

I brought some of my usual gang of geocachers. (They even bought me a
GPS as a group birthday gift). They really loved the clues and puzzles
aspect. This may convince them to try more letterboxes.