Here's email I received today, followed by my response. (Name withheld)
Is there any way that you would publish a mystery/puzzle cache without there being an actual container? The whole point would be to get pictures of Cachers from around the world without them having to travel to the actual cache. The one that I want to put out would be to get people to take a picture with there favorite rock or rock formation, and post it in there log, and then it would count as a find. So it would be sort of like a virtual or locationless earth cache, but it would be posted as a mystery cache.
Hope to hear from you soon.
Thanks for your email. Sorry to say that this type of cache cannot be published on geocaching.com. There has to be a physical cache for people to find and a log for them to sign, as per the guidelines. I'm not sure how
long you have been geocaching, but a few years ago there was a category of geocaches called "locationless", which the cache you describe would fit into. The cache owner would stipulate what the requirement was to log a find: see a yellow Jeep, find a Kent Feed sign, etc., and then post the coordinates where you saw it. Those cache types are no longer allowed to be listed on geocaching.com.
