This map picture will serve you much better than the google map above once you get close. There are two carparks. The first one must be very useful when the flower gardens are in bloom (reportedly quite beautiful) and is close to the tent site. The second carpark is the one where you should park if you want to climb the mountains in this post.
There are shorter walks between and around the carparks that are quite nice.
Kengamine is about 2 1/2 hours return. Its a beautiful walk through green forests with great panoramic views (its _frequently_ cloudy). There are two tracks from the parking area so you can walk up on one path and back down the other. There is a pretty little temple in a rocky area about 1 hour walk in which you may assume to the top but actually the top is a little way further. The temple is the most beautiful part and the right place to stop for a meal if you plan to stop. The temple is also the place where the two tracks from the parking area meet up.
After Kengamine the walking gets a bit harder on the way to Shakagatake. We thought it would be a nice short walk. Its not. The return walk is probably a bit over 4 hours from the carpark. Also the maps along the trail are not that good. There will be two unexpected junctions along the way. Just turn left at both junction on the way in and you will get there. Apparently, there is a shorter way to get to Shakagatake but we don't yet know where that starts from.