The geocache is not at the posted coordinates. To find it, you must complete the Painting the Town Adventure Lab and get the clues.
Once you have completed the 5 locations of the Adventure Lab, you will have the information necessary to get the final coordinates for this bonus (mystery) geocache.
At the completion of each lab stage you will see a photo which has the number that plugs into the letter for the final coordinates:
N 39 28.A6B W 86 C.D1E