It's said that the traditional fallas has its origins in Middle Ages when people used to celebrate St. Joseph Day (19th March), this religious festivity was mixed with pagan customs and both were accepted and adapted by the Church. Other people think that the party was originated by craftsmen of the zone when they used to burn the remains of their workshops; then it was acquiring human features and the first falleros artists were born.
If you travel to Valencia during the fallas festival (15th to 19th March) you'll enjoy a wonderful planning of several official events and other activities unscheduled at the street, where most action is located. You must be prepared because these days it's almost impossible to drive a car or even walk in the city because of the celebrations of this and other festivals such as the Father's day, Saint Joseph's day (Jesus' father), The Virgin de los Desamparados and the popular bullfighting.
You can appreciate in following images a bit of the huge celebration that takes place in the entire Valencia; the fallas has become an important tourist attraction in Spanish culture for locals as well as for foreigners.