There are a lot of Hidden places in Himachal. These are the most pristine places as tourist footfall is minimum. To know about these places you need to explore valleys and when you find it, just make sure you keep it pristine as well. Giriganga near, Bagasarhan near Rampur, Ropa in Spiti, hell lot of small treks near Manali to name a few. Let me know if it's helpful. Cheers and Happy travelling.