Hi Sainath, some of the popular solo destinations near Delhi are Bir-Billing, Kasol, Dharamkot and Khajjiar. If you want to go to slightly off-the-beaten-path hill stations then the options are Kausani, Naukuchiatal, Gushaini and Parwanoo. You can also refer to the attached article for more hill station options near Delhi. Since it's your first solo trip, I recommend, Kasol or McLeodganj.
Hey,
Since Delhi is cardinally located to many great places, you have a lot of options to explore, even if it is raining.
Agra, Jaipur, Kullu, Manali, Kasol are some of your options. For a 3 day Kasol-Manikaran-Kalga itinerary, check the following link out.
Hey Sainath if your planning to visit hills then i will recommend you spiti valley here is the full details have a wonderful and safe journey fellow traveler
https://banbanjara.com/cities/spiti-valley