Hey, September is an ideal time to visit both North India and South India. If you want to have an adventurous solo trip, head to Himachal and if you want to have a relaxing and peaceful trip getting along with people, getting to know them or their culture, want to be in nature's lap, then south India is the place for you. For more help in planning your trip to Himachal, DM me. More than happy to help?
Head over to Spiti, it is ideal. The tourism there extends there till November first week. August is the month of heavy downpour and landslides in Himachal. But September, you see, is the ideal blend of clouds and sun. You'll cherish each and every moment. Let me know if you have any queries on this. Happy to help.