The cache is not located at the posted coordinates. This is, however, a good place to park. The car park can be entered via Wason Street or Myrtle Street.
This is a bonus cache for the Adventure lab "Historic Milton". Once you have completed the five stages of the adventure lab then you will receive the actual coordinates
You can download a .gpx file containing the lab caches from here
Congratulations to Bonfire7 for the FTF