A Virtual cache is a type of cache that has no physical container. This is usually done because it would be inappropriate to place a physical container at the location. Reasons for this include:
- area is of historical importance
- area of cultural sensitivity
- it's an environmentally sensitive location
- the land owner does not want caches left there
- there is generally no room for a decent sized cache ( a Multi-cache might still be suitable)
The last point can be countered with an offset of multi-cache where you collect some information from the place of interest and then head somewhere else to find the container. That will depend on how far you need to travel to get to the actual physical cache. Quite a few people will expect it to be within walking distance, but that's not always possible. Multi-caches are not quite as popular as traditional caches and virtual caches probably fall behind Multi-caches in the range of popularity.
As a rule of thumb, most people prefer the physical cache to a virtual cache, so wherever you get the chance to list a physical cache, the community would appreciate those a lot more than a virtual cache. The ultimate choice on whether to list a virtual or physical (Multi-cache) reside with the cache placer.
Logging a virtual caches usually requires proof that you have visited the location, usually in the form of a photograph containing your GPS.
This graph demonstrates the hide / find counts for Virtual caches. http://geocaching.com.au/stats/graphs/gca/au/2100_cumulative_hides_finds_virtual