Each year, about a month after Christmas, hundreds of torch-bearers in an assortment of silly costumes march through the streets of Lerwick to set fire to a viking longboat. Welcome to the Up Helly Aa.

Up Helly Aa is a relatively modern celebration that seems to have its origins in the simple desire to get nuts and have a wild party. The official website of the celebration dates the start of the tradition back to 1880 when some organized revelers instituted a series of customs onto a messy yuletide celebration that rowdy soldiers returning from the Napoleonic Wars had begun years earlier.

While the specifics of the festival have evolved over the decades, the essential format has remained the same. Participants, known as "guizers," get together to form dozens of squads, each with their own costuming theme. As night falls on the day of the festival, each man is outfitted with a blazing torch, and the whole procession (which can reach up to 1,000 strong) marches through the streets in a fiery parade. Led by the officially appointed "Guizer Jarl," the festive army then surrounds a full-size replica of a viking longboat, and toss all of their torches into it, setting the ship ablaze.

The themes of the squads range from men in dresses to questionable racial stereotypes to Star Wars Stormtroopers, but the guizers of the Jarl's squad are always dressed like vikings. Being named jarl and being in his squad is a local honor and costume preparations for those in the lead group begin over a year before their appointed Up Helly Aa.

Even with all of the ritual and burning stuff, the revelers in an Up Helly Aa still find time to get good and rowdy, filling public halls all over the city as the squads perform entertaining little acts. If only all historic festivals seemed like such a good party.