Caches, that seems to be a great idea. It can be the challenge of the listing or the container itself. Something is very very special and very very rare - Have fun!
About Bookmark Lists
A bookmark list is a user defined collection of listings. They can be used as to do lists, watch lists, a way to organize listings you find, or whatever you decide. You can keep them private or share them with others.
Bookmarks can be added on the page for the listing or on this page using the waypoint name.
Bookmark names may be different than the actual listing. Click on the listings to see the actual names.