Natsu-matsuri. Matsuri 祭り (or just 祭) means festival, and natsu 夏 means “summer.”
In Japan, summer seems to start around July 15th, and so does the matsuri season. In Okinawa, there are usually multiple matsuri every weekend through September. Almost every Saturday and Sunday night the sky will be illuminated by fireworks (hanabi 花火) and the sounds of Okinawan eisa dance (エイサー) echo in the night air. In Okinawa, you will see the strings of Orion lanterns illuminating the paths and and smells will waft from the tents hawking foods.
Every town and village will host their own matsuri; men and women, from children to older folks will wear yukata 浴衣 and jinbei 甚平. Even I own a very classy black jinbei with Hello Kitty x OnePiece on it. Err, well, it is sort of tomboyish, but I find it cute and comfortable… I am pretty sure I would feel weird in a girly yukata. As a note, many westerners do not seem to realize the difference between kimono 着物 and yukata 浴衣. Kimono is very formal and layered, it would be odd to see kimono outside of formal events like weddings, graduations, or New Years Day. Yukata are light and thin, perfect for summer! They are more casual and are easier to put on. And wayyyy cheaper! Formal kimono are usually thousands of dollars (and therefore many people simply rent them instead of buying).
There are performances, games, food, and of course drinks of the alcoholic variety! Oh and they always hand out fans (うちわ uchiwa) as a means of advertising.
If you are in Okinawa or Japan during the summer season, you must attend one.