Mega-event cache
From Cacheopedia
A Mega Event Cache is similar to an Event Cache, but it is much larger. In order to qualify as a Mega Event, the event cache must be attended by 500 or more people. Typically, Mega Events are annual events and attract geocachers from all over the world. The pages of a Mega Event mark the location, date, time, description, requirements, etc. of a geocaching event, just as in the case of a regular event cache. For paticpating in a Mega Event, a geocacher is able to log and receive a Mega Event icon to add to their cache counter.