letterboxer

noun

let·​ter·​box·​er ˈle-tər-ˌbäk-sər 

plural letterboxers

: a person who engages in letterboxing (see letterboxing sense 2)

Connolly … is a letterboxer. Part hiking, part puzzle solving, part treasure hunt, letterboxing has become an obsession for people who enjoy physical and mental workouts.

—Deirdre Van Dyk

Word History

First Known Use

1984, in the meaning defined above