Durga Puja
If you are planning to travel to Kolkata the right period of the year is in the end of September, beginning of October. The Durga Puja is a holy festivity celebrating the victory of the Goddess Durga on a demon.
It is the main holiday of West Bengal, the city is full of temporary temples made of bamboo.
Indian people told me it is like our christmas but it has nothing to do with it...