Since geocaching is a new activity governed only by the general agreement of people in online discussion groups, it is always changing. Variations include "travel bugs," which are objects with tags that ask finders to move them to new locations, which are then tracked online. "Multi-caches" direct finders from one location to the next until they locate the actual cache. "Virtual caches" are located in parks or environmentally sensitive areas where physical caches are not appropriate. These are usually landmarks, such as monuments or historical markers.