The next information will be taken from Wikipedia.
"Formerly, much time would be spent by the Casal faller preparing the ninots (Valencian for puppets or dolls). During the four days leading up to 19 March, each group takes itsninot out for a grand parade, and then mounts it, each on its own elaborate firecracker-filled cardboard and paper-mâché artistic monument in a street of the given neighbourhood. This whole assembly is a falla.
The ninots and their falles are constructed according to an agreed upon theme that has traditionally been, and continues to be, a satirical jab at anything or anyone who draws the attention of the critical eyes of the falleros—the celebrants themselves. In modern times, the whole two week long festival has spawned a huge local industry, to the point that an entire suburban area has been designated the City of Falles – Ciutat fallera. Here, crews of artists and artisans, sculptors, painters, and many others all spend months producing elaborate constructions of paper and wax, wood and styrofoam tableaux towering up to five stories, composed of fanciful figures in outrageous poses arranged in gravity-defying architecture. Each of them is produced at the direction of one of the many individual neighbourhood Casals fallers who vie with each other to attract the best artists, and then to create the most outrageous monument to their target."
On the final night of Falles, around midnight on March 19, these falles are burnt as huge bonfires. This is known as the cremà (the burning), the climax of the whole event, and the reason why the constructions are called falles ("torches"). Traditionally, the falla in thePlaça de l'Ajuntament is burned last.
Many neighbourhoods have a falla infantil (a children's falla, smaller and without satirical themes), which is held a few metres away from the main one. This is burnt first, at 10:00 pm. The main neighbourhood falles are burnt closer to midnight; the burning of the falles in the city centre often starts later. For example, in 2005, the fire brigade delayed the burning of the Egyptian funeral falla in Carrer del Convent de Jerusalem until 1:30 am, when they were sure all safety concerns were addressed.
Each falla is laden with fireworks which are lit first. The construction itself is lit either after or during the explosion of these fireworks.Falles burn quite quickly, and the heat given off is felt by all around. The heat from the larger ones often drives the crowd back a couple of metres, even though they are already behind barriers that the fire brigade has set several metres from the construction. In narrower streets, the heat scorches the surrounding buildings, and the firemen douse the façades, window blinds, street signs, etc. with their hoses to stop them catching fire or melting, from the beginning of the cremà until it cools down after several minutes.
Away from the falles, people frolic in the streets, the whole city resembling an open-air dance party, except that instead of music there is the incessant (and occasionally deafening) sound of people throwing fireworks around randomly. There are stalls selling products such as the typical fried snacks porres, xurros and bunyols, as well as roasted chestnuts or trinkets.
The five days and nights of Falles are a continuous party. There are a multitude of processions: historical, religious, and comedic. Crowds in the restaurants spill out into the streets. Explosions can be heard all day long and sporadically through the night. Foreigners may be surprised to see everyone from small children to elderly gentlemen throwing fireworks and noisemakers in the streets, which are littered with pyrotechnical debris. The timing of the events is fixed and they fall on the same date every year.
During Falles, many people wear their casal faller dress in regional and historical costumes from different eras of Valencia's history
I went to Valencia with my mother in 2009 and arrived the week following Falles. I had no clue that this even existed. I felt we had missed out on it. We went to the Falles museum where they save one ninot from the fire and place it into the museum. I really enjoyed it as the ninots are like nothing I had ever seen. The artistry of capturing the expressions was amazing. There were so many funny ones. I enjoyed seeing them but it was only a small taste of the festival so I would really like to attend it one year.