Pre monsoon months of April- may is always good to head to the mountains. This is the time when the snow has not yet melted fully. It’s pleasantly cool. Also it’s the time of Rhododendrons.
If you like trekking, Sandakphu is the trek you should consider this time. Check out this Sandakphu blog, though its without Rhododendrons at that time.
https://www.tripoto.com/trip/most-rewarding-most-pocket-friendly-trek-sandakphu-60671dc6576b9
Manali, Himachal Pradesh, India. Goa, India. Shimla, Himachal Pradesh, India. Kerala, India. Andaman and Nicobar Islands, India. Darjeeling, West Bengal, India. Munnar, Kerala, India. Gangtok, Sikkim, India.
Go to rishikesh and do rafting and camping is really fun and relaxing for you or either you go spiti valley see some mesmerizing view and feel the peace .