I'm always trying to come up with some unique challenge ideas. I got this one while looking over stats on Project-gc.com. I noticed a second calendar grid displayed there. Pretty much every cacher I know has either done or is working on the 366 calendar challenge to find a cache on every day of the year. This is an off-shoot of that, similar to a Jasmer challenge.
To log this cache you must find a cache placed on all 366 possible dates.
I completed this grid totally by accident, so I'm not sure what the difficulty of this may be. Project gc offers a tool to help you find any missing dates you may have. I'm guessing this would be easier than the 366 challenge simply because you can find these caches on any date. It's also a calendar grid you can complete without having to wait for a leap year! Simply post your completed calendar to show you qualify for this one.
The cache itself is a peanut butter jar hidden in a typical manner. May not be totally winter friendly.