Shimla, kullu and Manali
and plan going to shimla by toy train from kalka railway station (around 5hrs journey from Delhi) it's an UNESCO reognised and the journey will amazing with beautiful stations almost like disney
I suggest you to visit Mysore, Karnataka during Dasara . The palace and whole city will be decorated with lights ,and Mysore is very clean and less jam packed city . try being there on Dasara