There are number of places to be explored in Monsoon
In Rajasthan
Bundi
Udaipur Kumbhalgarh in Madhya Pradesh
Panchmarhi Mandu In Maharashtra
Konkan area Sindhudurg
Malvan
Ratnagiri
Ganpatiphule Raigadh in Gujarat Saputara
Starting with
Kerala you could explore
Munnar
Asthamudi
Idukki
Wayanad and Kumarakom. In Karnataka monsoons are great to watch at
Coorg
Kudremukh
Chikmagalur
Mysore and Kabini Moving towards Maharashtra Lavasa
Lonavala Khandala Mahabaleshwar
Malshej ghat
Matheran Kaas plateau Raigad Pune Moving towards uttarkhand
Nainital
Mussorie
Dehradun
Almora In Himachal Shimla Manali Chopta Mcleodganj While all over north east Meghalaya
Sikkim
Darjeeling Manipur
Mizoram are some lovely monsoon spots.
Depends from where you are traveling. monsoon are best to explore waterfalls and greenery mountain areas
Jog falls, Dudhsagar, Bedhaghat, malsej, lonavala, augumbe, Chikamangalur, etc are good places to visit
Western Ghats, around pune. so many trekking places, Rajgad to Torna is my favourite, you can also visit, lonavala, prabalgad, kalavantin. bimshankar. and so on.
Hi, you can visit Chikmagalur Ooty Munnar waynad for a chilly weather and a nice monsoon feels. These places are not very crowded and the food is also remarkable.