To log this locationless cache, you must post a haiku in your log entry that deals in some way with geocaching. There is no terrain to negotiate except the inside of your own skull. The only difficulty is in generating a haiku which fits the criteria listed below.
A haiku is a Japanese verse form, notable for its compression and suggestiveness. It consists of three unrhymed lines of five, seven, and five syllables.
As an example, here is one that I wrote this afternoon:
Just one last waypoint!
GPS batteries die.
No one hears your screams....
A more precise and comprehensive definition of the haiku form can be found online at this page.
Alas, some of the best haikus that I have ever heard are off color, raunchy, or occasionally, pornographic. If your haiku falls in this category, please remember that geocaching is a family sport -- children of many ages read this site and are fully capable of hitting the decrypt link or following links to your own website. I don't know if geocaching.com has an explicit policy on this matter, but I'd prefer that you not enter such an entry in your log. If you feel that your contribution must somehow be propagated to the greater geocaching community, e-mail represents a much more precise tool for spreading material to specific people who shares one's tastes.