- Letterboxing North America
 - Provides access to letterbox clues throughout the New World. - Letterboxing.Info
- Dedicated to the activity that combines elements of a scavenger hunt, hiking, orienteering, map reading, puzzle solving, and creative expression.
- Atlas Quest: International Letterboxing
- Dedicated to the pastime that combines artistic ability with treasure-hunts in beautiful, scenic places.
- dartmoorletterboxing.org
- Guide to letterboxing, an outdoor pursuit with similarities to orienteering, out on the moor.
- Letterboxing in Germany and Continental Europe
- Letterboxing how-to guide that offers clues listed by federal state and European nation.
- Valley Quest
- Series of treasure hunts, based on a 150-year old British model, that leads to the Vermont's unique places.
- South Western Ohio GeoCachers (SWOGO)
- Dedicated to geocaching and letterboxing in South Western Ohio.
- Urban Letterboxing
- Transplanting the leisurely countryside activity to major cities around the world. Includes a letterbox database and a list of what one needs to start letterboxing.
- Dartmoor Letterboxing Pages
- Tips on locating the letterboxes, hidden boxes containing a stamp and a notebook, of Dartmoor Park.
- Letterboxing USA
- Features an interactive map with clues.
- Dartmoor Letterboxing
- Learn about the history of letterboxing in South Devon's National Park. Also home to the informal Letterbox 100 club.
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