This cache is at the location.
As a challenge you have to have completed the Quartz level of the Discovery Awards for Earthcaches. That means you have found 50 Earthcaches
I can check it by looking at your stats. Feel free to sign the log, but do not log as a found until you have completed the challenge.
Thanks to Rikitan for writing a checker.
Ba gur sraprcbfg, fznyy ghor.