Hey, go for Jaisalmer , Udaipur , jodhpur as december is the best time to visit . Or else go for goa and spend romantic time on beautiful beaches. another option would be andaman and nicobar islands . This would be the perfect romantic as well as adventurous visit . Or can Visit Agra for the love icon Taj mahal too.
Happy planning..!! happy journey..!!
If you are planning for hill station you can go to manali or a Jammu
or if you are planning for a south trip I suggest you Kerala will be the best place to visit in dec .