If you are looking for nature then I would suggest Laitlum and Cherrapunjee in Meghalaya for summer trip. Dawki is another place you can go to here but its best to Visit Dawki in December. as you can experience the beauty of Umngot river where the water is so clear that you can actually see the river bed. Another place that suits your requirement is Dzukuo Valley in Nagaland. Words fail to describe the beauty of this place.