I'm sitting on about 20 unused keys from my Humble Bundle account for games that I probably won't get round to playing. How about this for a fun treasure hunt:
I can write the key on a piece of paper and hide it in a location. I can take a screenshot and provide a cryptic clue in the forum - it then becomes a free for all to find it and redeem the key on steam. I can stash the paper inside a barrel which if I recall correctly would give you guys 9 days before it despawned.
Anyone interested?