An earthcache is a location(-cache) about a unique geological feature, where you have to answer some questions and thus learn a bit about the earth.
The Earthcache Masters programme is an additional reward system -ontop of the usual smiley- and has four levels: Bronze, Silver, Gold and Platinum.
More about earthcaches and the master programme at earthcache.org
Earthcache Master Platinum level reached on 29 may 2010.
Bronze level reached: 3 finds in 2 countries.
Developed 09/12/09 Norway GC21N8F Dorgefossen
Silver level reached: 12 finds in 4 countries and 1 developed.
Developed 07/03/10 Sri Lanka GC22Y4T Ritigala - A Himalaya fragment on Sri Lanka?
Gold level reached: 16 finds in 4 countries and 2 developed.
Developed 08/03/10 Qatar GC22YG4 Got Vinegar?
Platinum level reached: 20 finds in 6 countries and 3 developed.