Mystery cache
From GeoWiki
The Mystery cache (also known as an Unknown or Puzzle cache) is a "catch-all" type for caches which don't fit the definitions of the other cache types. Examples are caches involving puzzles you need to solve to determine the actual coordinates, sending the cache owner a verification codeword found inside the logbook, performing some task at the cache location, or writing the online log in a format or with content that satisfies the cache requirements. Sometimes the hider may decide to declare a mystery cache just to add an element of surprise, or to remove any pre-conceived ideas about the hunt.
