If you want go to some remote and less crowded place and interested in trekking then you could choose tirthan valley. There are lot of places you could visit in tirthan.
From tirthan Manali is also approx 50kms. And tirthan valley is very beautiful.
Visit Ramnagar and try to go nearby hilly areas ..its completely untouched and less crowded.Check my blog for more info.Bir is another good option visit ,don't forget to visit tea plantations in Dharamsala
Hey Rohit, Summers in Delhi are difficult to tolerate. If you are looking for unexplored places, I'd suggest you Tirthan Valley, it is one of the offbeat places in the Himalayas. If you plan to visit there you can book your stay in advance in Raju Bharti's Guest House, it is one of the best places to stay in Tirthan Valley. If you are fexible with number of days you can go for Spiti Valley, it will be a great experience if you take a circle and travel Spiti Valley via Kinnaur Valley and return via Manali covering Chandratal.