This is a bmp and is not the same image as the one in the gallery.
One of a series (Watermark level xx) in which it gets steadily harder to solve the puzzle, though there is a common theme to them all. The size and difficulty of the cache hide varies throughout the series. There is also a passphrase in each puzzle which will be some help with the next puzzle in the series. It is strongly recommended that you solve the previous level before tackling this one.
The commentary is encoded in a similar fashion to ROT13, but instead of moving on (encoding) or back (decoding) 13 places, the move on (encode) or move back (decode) is defined by repeated copies of the passphrase - A=1 position, Z=26 positions.
EG if the passphrase is "C'a d", then use "CADCADCADCAD..." or 3,1,4,3,1,4,3,1,4... to shift the text. So "watermark" is encoded as w+3=z, a+1=b, t+4=x, e+3=h, r+1=s, m+4=q, a+3=d, r+1=s, k+4=o which is "zbxhsqdso". There is an online decoder available now.
Wpmc pdrooaj vwz gitexy ywbiilm nu hdl btaylnr an ticw jjirldq vhm thuhs xnztgg, xnrnh'c adpb npj ftxcxdq dgjud xg nwt.
The cache is initially stocked with several bits of frippery and there is a "First To Find" trophy. The trophy went to timhewison of Frankfurt in Germany - congratulations. The terrain is based on walking from the icon to the cache.
Good hunting. You may also be interested in my other caches.