In May 2004, I planted a letterbox in El Ranchito. Since the facility is rather park-like, it isn't easy finding a good place to hide such a thing, but I did my best. The letterbox turned out to be reachable by Brownies, who are more persistent than I gave them credit for!
The stamp (shown above) was intended to look like a forked stick with two marshmallows on it -- double s'mores!
Unfortunately, the letterbox disappeared sometime in mid-Summer 2005. It will be replaced shortly, with a newly-designed stamp.