Hey Chiranjiv, Much unexplored places in North east are :- Ziro in Arunachal Pradesh Tawang in Arunachal Pradesh Majuli island in Assam Loktak lake in Manipur Bomdila in Arunachal Pradesh Vantawang waterfalls in Mizoram These are few unexplored places in Northeast ... Happy Travelling !!!
Hands down... Arunachal Pradesh!! Mechuka is the least visited, unexplored last town in Arunachal Pradesh near the Indo-China Border. So remote you will be out of connectivity for days. To learn more about mechuka, head to my profile, I have written a detailed blog on what to do and see in Mechuka.
Go to North sikkim;It is Untouched heaven on earth.Believe me,the path that goes to Gurudingmar lake will appear like You r going to heaven.When You will reach the lake,your eyes will be mesmerized.