Florence's tradition is called Scoppio del Carro ("Explosion of the Cart"), and it occurs in the Piazza del Duomo every Easter Sunday at noon. It's a very old tradition, whose origins can be traced as far back
as the First Crusade in 1099. That’s a lot of exploding carts. Here’s what happens:
It starts with a grand procession, in which a team of oxen decorated with flowers pulls an elaborate cart through the streets of Florence. The oxen, who are accompanied by soldiers, musicians and people dressed in 15th-century garb, pull the cart all the way to the Piazza del Duomo. Once there, a wire is attached, which extends from the cart to the Cathedral of Santa Maria del Fiore. Then, at the key moment during Easter mass, the Archbishop lights a dove-shaped rocket, which travels along the fuse all the way to the cart, lighting the fireworks inside and setting off an elaborate 20-minute pyrotechnics display.
According to legend, if the burning of the cart goes well, it means a prosperous year for Florentines. This probably harkens back to a quasi-pagan tradition hundreds of years ago, when the locals hoped for a good spring harvest.
Anyway, if you aren’t going to be in Florence this weekend, you could always try for next year. I’m not sure when Easter falls in 2011, but whenever it does, you can bet a cart will be exploding in Florence.