Old Mother Hubbard is an old English nursery rhyme, first published in 1805 but with origins older than that.
There is about to be a bit of a nursery rhyme revival in the FB household with FB5 starting to show lots of interest in age appropriate literature.
This cache is where OMH's dog would have liked there to be a bone. Oh dear, no bone but there is a cache, that will have to do.
Svsgl/svsgl punapr lbh'yy or evtug svefg gvzr.