Every year, around the 14th or 15th of January, a small festival is held in the dark hours of the night on Oiso's "Long Beach," which is most popular in the summertime for swimmers. However, if you were to stumble upon this usually quiet town on this particular evening, you would be greeted with bonfires 7-8 meters tall, and festival-goers in the throes of a yearly tradition.
Around town, those who belong to an "omikoshi" group (an omikoshi is a small portable shrine that is carried through the streets) gather at homes to eat, drink, and mentally prepare for the festival that starts promptly at 7 pm. You may ask, "Why would one need mental preparation for a festival?"
Well, at 7 pm, the bonfires are lit, and the festival gets going. This is a family event, and includes people who have been attending since childhood. Many of the children participate by roasting "dango," small delicious balls of glutinous rice. Dango is eaten with the hopes of good health for the upcoming year.
There are many bonfires on the beach, and the flames can get quite large. Make sure to wear clothes that are warm and easily washable. The smoke can be overpowering, so be prepared to go home smelling like it! From each bonfire group, there are several men who have volunteered to don traditional loincloths and plunge into the frigid ocean. (This is the part that requires the most mental preparation - usually in the form of drinking copious amounts of sake). After being dragged out of the ocean on a small wooden sled, they are subsequently paraded around town (still on the sled), dragged along by other festival-goers. At some point, the sled is taken to a shrine, where those still in attendance eat some tofu. Throughout the whole process there is lots of song and drink, so even if you are just an observer it can still be a lot of fun.
Whether or not you decide to follow the die-hard Sagicho-ers, it's worth going. The bonfires provide some warmth, and the flames are quite spectacular.