I was hiking the Isabella Trail and I decided that this was a nice place for a cache. Depending on how you do this cache, the difficulty/terrain will vary. The longer (and more adventurous) way would be hiking the Isabella Trail. The trailhead is located in Potato Patch. If you decide to do the hike (which is fantastic! definitely recommended), out of Prescott, go south on Walker road. When the road becomes a dirt road, you will reach a fork, take a left (by the primitive road sign). Then follow the windy road for a little while and the take a right when you reach the welcome to Potato Patch sign and follow the road a short distance (about a quarter mile). The trailhead will be on the right side (when the road curves left, the trail is the right-hand one, after a short ways, a cairn will be on the left). The hike is about 6 miles round-trip, with an elevation gain of about 950 feet. I would rate the terrain on the hike a 3.
The other method (for the lazy people 
) is taking a road all the way to the summit (there is a lookout tower here). **Thanks to Lightning1996YCJP for these directions** To get there by driving, take the Senator Highway (Forest Road 52) south out of Prescott. Turn onto Spruce Mountain Road. Follow the road all the way to the top (if the gate to the top is closed, it is a half mile walk up the road to the summit). I would rate the terrain using this method a 1.5.
The cache itself is located a short distance from the tower, just follow your GPS from there, and you will be fine. The container is rectangular shaped (spray-painted black) and is big enough to hold quite a few items. I started it off with some various toys.
Good Luck and Enjoy!