The cache is not at the posted coordinates.
This is a bonus cache for those completing the
Adventure Lab.
The coordinates will reveal themselves upon completion of the Adventure Lab.
After completing the last (most southern) leg of the Adevnture Lab Cache, it should be a short walk to this bonus cache. Take care with little children as the sidewalk ends and there is a bit of a blind curve.
The terrain rating is primarily due to the length of walking to complete the Adventure Lab Cache.