The Cultural Festival (文化祭 Bunkasai) is a festival at North High and other Japanese schools where all the students go off and show their talents. At North High it took place in November.
In The Sigh of Haruhi Suzumiya, due to the disappearance of class representative Ryoko Asakura, Haruhi Suzumiya and Kyon's Class 1-5 simply did a survey. This prompted Haruhi to write a movie, The Adventures of Mikuru Asahina Episode 00, which the SOS Brigade planned on displaying at the event. In addition, the Computer Research Society wrote a game, The Day of the Sagittarius III, which they also displayed at the event. Itsuki Koizumi's class put on a play, Yuki Nagato did "fortune telling" for her class, and Mikuru Asahina and Tsuruya worked at a fried soba cafe.
Behind the Scenes
In real life, most schools hold the cultural festival on or around Culture Day (文化の日 Bunka no Hi) on November 3rd, a national holiday. Normally the festival is held on a Saturday or Sunday, sometimes even both.