Letterboxing

 Letterboxing is an outdoor hobby that combines elements of orienteering, art, and puzzle solving. Letterboxers hide small, weatherproof boxes in publicly accessible places (like parks) and distribute clues to finding the box in printed catalogs, on one of several web sites, or by word of mouth. Individual letterboxes contain a notebook and a rubber stamp, preferably hand carved or custom made.

рuzzlehunt

 A puzzle hunt (sometimes рuzzlehunt) is an event where teams compete to solve a series of puzzles, many of which are tied together via metapuzzles. Puzzlehunt puzzles are usually not accompanied by direct instructions for how to solve them; figuring out the necessary approach is part of the puzzle. These hunts may be hosted at a particular location, in multiple locations, or via the internet.

Sangaku

 Sangaku or San Gaku (算額; lit. translation: calculation tablet) are Japanese geometrical problems or theorems on wooden tablets which were placed as offerings at Shinto shrines or Buddhist temples during the Edo period by members of all social classes. 

 

rebus

 A rebus (/ˈriːbəs/) is a puzzle device that combines the use of illustrated pictures with individual letters to depict words or phrases. For example: the word "been" might be depicted by a rebus showing an illustrated bumblebee next to a plus sign (+) and the letter "n". It was a favourite form of heraldic expression used in the Middle Ages to denote surnames.