Let's start with the underlying structures, like good social historians. The city of Valencia (population 800,000) is divided into some 500+ geographically based clubs. These have a club house, the Casa Faller, which is some kind of social centre, function room or bar. Often the area served by each Fallas club is only a couple of streets, a really small neighbourhood. They cover the historic centre and all the suburbs too. They operate year round as a meeting place: old men sit there playing cards, they host after school clubs and kids' activities, they host cheap communal meals, parties, enormous paella cook-offs, social support structures for the elderly and isolated, fund-raising for charities etc. The are, in short, a formalised manifestation of highly cohesive local communities. In some ways they might be comparable to parishes or Italian contrade, but they don't necessarily have a strong historical basis – though some do – since new fallas clubs can be set up at will. They are small, by character areligious though they may have religious links, and a traditionally entirely working class phenomenon.
Each club produces one or two 'fallas' each year (as does the town council, pictured above, always one of the largest). These are huge colourful statues/ sculptures, traditionally made of wood and papier maché and then painted. Nowadays they often have styrofoam or plaster of paris or wax or who knows what other materials as well. Most clubs make one large adult falla and a smaller one for/by the kids, the falla infantil. Once made exclusively by the members of the casal faller, nowadays various artists and artisans are drafted in to help or to supervise. They can reach over 20m in height, even 30:
and are erected in piazzas, on street corners, in whichever tiny space can be found to cram them into. They can be on whatever theme or subject you like – traditionally many have carried satirical messages on political or social issues, whether local or national which are further driven home by small placards with (often rhyming) mottos written in Valenciano, the local dialect (a version of Catalan, though don't let the locals catch you saying that.) This year, by contrast, a very large number had some kind of marine and/or naval theme, in honour of the Americas' Cup which is to be held in Valencia this June. Or complex variants on marine themes, like Odysseus and the Sirens:
The process of designing, building and painting these amazing works takes all year, and can cost an incredible sum: this year's winning falla club spent €750,000 on its two pieces. THREE QUARTERS OF A MILLION EUROS. Imagine. Most cost less though: there were some 720 built this year, between full-size and children's versions, and few will have cost anything even approaching this amount.
(there were a lot of bare breasts on display in this year's fallas, I must say)
The fallas are built in secret and erected at midnight, a week before St Joseph's Day. Then, on the night of the 19th, shortly before midnight, they are all burned. This is the 'cremà' (which I guess comes from the same linguistic root as cremation). A string of bangers acts as the fuse, and the whole thing goes up in smoke, burning away over maybe half an hour or an hour. Firemen attend those which are most in danger of setting fire to trees, buildings, the general public etc., and hose them down as needed. The ashes are cleared away almost immediately, by the following morning you'd never guess there was anything there, and the whole process starts all over again.