The cache IS at the posted coordinates. This is a challenge cache.
The Challenge
The challenge is called "The Least Accessible Challenge" because it involved Terrain 5 cache finds, which of course are very difficult for most cachers to access.
In order to log a find, you must have at least 25 caches in EACH of your nine Terrain 5 grid squares.
The Rules
Once you have signed the logbook and the Project-GC checker confirms you have completed the challenge, you can log it as Found. Until then you may post a note if you have only signed the logbook, and claim a find once you qualify. Good luck!