The possibilities are endless, depends upon the connectivity.
try the Exploration of Nanital region i meant all the lakes., i mu self covered 4 lake in 3 days. best being Naukuchiya tal and Saatal and ofcourse tye Nainital.
In my opinion, you must select Kerala as your destination. The climatic condition of Kerala is divided into three summer season, winter season and monsoon. In December Kerala experience winter season. So you can visit beaches in Kerala. You can go for a houseboat cruise through backwaters in Kerala. You can do trekking to the forest, you can swim in small pools near the waterfalls in Kerala. You can visit Fort Kochi, Padmanabhapuram Palace, Sree Padmanabhaswamy temple etc. You can variety of Kerala foods and also watch Kerala traditional art forms