Letterboxing & Geocaching

Lately, I've been hearing more and more about letterboxing.

LETTERBOXING is an intriguing pastime combining navigational skills and rubber stamp artistry in a charming "treasure hunt" style outdoor quest. A wide variety of adventures can be found to suit all ages and experience levels.

I love treasure hunts. A lot of people seem to be into geocaching but it's a bit too high-tech for me so letterboxing seems right up my alley. Anyone do either one?