From 13 to 19 March, Valencia celebrates one of Spain's best known festivals: Las Fallas.
The Fallas are big models made out of papier mache, wood and wax, and often characaturing Spanish social and political current affairs. The models are burnt on the night of 19 March. Fireworks and firecrackers play a big paper in any fiestas in this region, and Fallas is no exception. Be careful of firecrackers being thrown along the street by youngsters. And be prepared for the ground to shake with the force of the fireworks which begins at midnight.
The are two teories about Fallas.
The festivals have been celebrated in Valencia since the Middle Ages when carpenters used to light a bonfire on 19th March, St Joseph Day. Joseph - José in Spanish - is the Patron Saint of Valencia, and St Joseph's Day is Fathers Day all over Spain. A second theory is that the tradition of lighting bonfires in honour of the saints where good for pagan people, which the Church accepted and adapted to its own interests.
The city is adorned in decorations and Fallas, and public enthusiasm takes to the streets. During the week the following ceremonies take place: the nomination and proclamation of the Fallas Queens, the Exaltation, the Crida, the Cavalcade of the Ninot, the Offering of Flowers, the Planta and the Cremá.
The Crema is the culmination of the Fallas.

credits: me & the fallas page...