August would be a good time to visit Himachal Pradesh. It is just a peaceful town on the National highway to Shimla. As I said, it looks beautifully green in monsoon time, Prashar lake is also one of the top offbeat places in Himachal to visit in August. Kullu Manali, Dharamshala, Shimla, Dalhousie, Khajjiar, Chamba, Chail, and Kufri are the best places to visit in Himachal Pradesh during the monsoon season.
You can visit any place except for Remote areas that are too far away from National Highways. August is a safe month but weather might play a spoilsport sometime.