The first geocache of this kind is GC357G1, which has been placed by the author of this cardridge. He also maintains a bookmark list of these geocaches which can be found here.
The concept itself comes from here, and you can watch the video to get a better understanding for it.
The cache itself is not on the posted coordinates. To actually find the geocache you need a device that can handle wherigo cartridges. It could be a smart phone or a dedicated GPS device. The cartridge itself can be downloaded here.
To be able to find this geocache, you will need these three codes which you will enter into your wherigo-software:
After that, your mission is to get within 25 meters from the geocache. When you are, the cartridge will tell you the exact final coordinates of it. Note that you only have 50 tries. But don't worry, most will make it in about 10, and if you should fail, you can just start again and will have a good heads start.
If/when you find the geocache, sign the log as usual. You will also be given a personal password so that you can create other geocaches like this one after solving one if its kind. Good luck!