This one is going to be tough. Cache is at coords but can only be logged when all requirements are satisfied. A short hike in the woods will lead to a hidden ruin. You can sign it when you find it but log only when you can prove it.
requirements
must have found 200+ unknown caches
vs lbh ernyyl dhnyvsl sbe guvf gura lbh jvyy abg arrq n uvag.