A hidden container with a few stashed trinkets, but more importantly, a lookbook for the finders to write about their "hunt", with an online depository of cache locations and virtual logs ... the idea of a mountain geocache is in a way a middle ground between the traditional summit log (conspicuous and sometime causing the ire of self-appointed environment warriors) and an SP log (only the virtual log remains, with little or no realspace confirmation).
Geocaching information is catalogued by a number of websites in various languages, some completely open to the public, others more restricted e.g. pay-per-view or approved members only. There are local associations in most big countries and regions, often with thriving regional websites.
Most of the hunt takes places in the lowlands of course. Environment minders need not worry too much about the damage from the hordes of geocache seekers, since the universally accepted rules disallow them from environmentally sensitive areas, or from being hidden in intrusive ways such us digging, etc ... and hardly more than a handful of people a year are ever looking for any of these "secret stashes" in the mountains.
I plan to add a few words and external links to this page, but the foremost need of this album is simply more images. Please add your own!