A Reverse cache is a type of geocache where a finder is guided to a specified location or target location. i.e. The box will help you to arrive at a specific location. At the location, either a log book is revealed to be signed (for example, a box can be opened) or a logging requirement (such as a description of the location or code) is made known to the finder.
In the few examples that are listed at Geocaching Australia the GPS-enabled box presents users with a deceivingly simple button and a small display. You press the button and the display reads a distance. Players only have a limited number of chances to move the box to the correct location before the box locks forever. At location 1 you might be given a distance of 2000m. You know know that the box will unlock on a circle with a radius of 2km from your current location, but where? Way too many possibilities. You move to a new location and press the button again. You are given a different distance, say 2100m. You now have two circles. The first based on your original location and the second at your current location.There are two places at where those circles intersect. The box will open at one of the those two locations. But which one? Move for a 3rd time and try again. The three circles will intersect at only one location. Find that and the box will open. In general the cache owner will provide instructions on their specific reverse geocache when you pick it up from them.
A Reverse cache is normally an electronic hardware device, utilising its own GPS location to determine how far it is from the target location. However, it could also be a software application or web page, which then utilises the GPS functionality in smart phones.
If you are going to publish a reverse cache, consider how people will contact you to organise picking up a hardware device. Please also consider how people will know when the device is being used by another cacher and therefore not able to "find" the reverse cache at that time.
Hints, Tips and Tricks
Making a physical hardware Reverse cache will be expensive to buy the necessary parts and some electronics and programming knowledge will be required to construct one. Also the device should be robust enough to survive being used by other cachers.