Believe it or not, there is a method to the madness and nothing is celebrated in Japan without a purpose. Even if you don't particularly care for the reason of the festival it's still a fun time, so enjoy yourself!
Kanamara Matsuri (The Penis Festival)
Of course, it wouldn't be a penis festival without penis merchandise. You'll see plenty of penis hats, lollipops, shirts, costumes and giant wooden penises being paraded around. There is also a contest for who can carve the best penis out of radishes.
Hadaka Matsuri (The Naked Festival)
The purpose of the festival is to gain luck and good fortune for the following year by grabbing a pair of lucky talismans thrown by priests. The men aren't naked, but wear a traditional Japanese loincloth that pretty much shows everything besides their genitals.
The festival begins at 12am when all the lights are turned off and the men wait for the priests to drop the lucky wooden talismans from the shrine. You'll know once they've been thrown into the crowd because you'll see everyone pushing and climbing on top of each other to grab the two wooden sticks. Once someone has successfully grabbed the sticks they will stick it in a box filled with rice and be deemed the luckiest man.
Along with the two stick there are bundles of other lucky items thrown into the crowd to create more of a challenge.
Naki Sumo Matsuri (Baby Crying Festival)
During the Naki Sumo Matsuri two sumo wrestlers each hold a baby, face each other and proceed to make weird faces and wear scary masks to make the babies cry. The baby who cries first, the loudest, or the longest is crowned winner. An official sumo referee judges the match.
The belief behind this 400 year old tradition is that the cry of a baby will scare away demons, granting them a long and healthy life.
Hokkai Heso Matsuri (Belly Button Festival)
The main attraction is the Heso Odori (Belloybutton Dance) where performers dress up, paint their stomachs with funny faces and compete for various pries. The heso (bellybutton) is often painted to look like a mouth.
Akutai Matsuri (Cursing Festival)
The festival takes place at the Saishoji Temple in Ashikaga on the third Sunday of December. Worshipers are led by thirteen people dressed as red-faced mountain goblins called tengu up Mount Atago to Atago Shrine. During the journey worshipers will yell curse words and insults.
The tengu will also make offerings at eighteen small shrines on the way up. Worshipers will try to steal the offerings while shouting insults and curse words, this is said to bring good fortune. After reaching Atago Shrine participants are blessed by the Shinto priest and the tengu toss rice cakes into the crowd.
Besides banishing evil, the paantu are also meant to scare kids. Similar to the boogeyman, the paantu are supposed to frighten kids into doing the right thing and follow the pure path.
The festival takes place on Miyako Island located in Okinawa. There are two versions of the festival, the one I've described is practiced in the Hirara Shimajiri area. The festival takes place in September.
The second version of the festival is located in the Ueno Nobaru area and takes place in December. Instead of men dressing up as Paantu, one boy is chosen to dress up in mud and leaves and walk around the streets with a group of women playing traditional drums.
Oga Namahage Matsuri
Before leaving, the demons scare obedience into the kids and repeat the process with another house. This isn't really a festival, but it's still a really weird tradition.
Takeuchi Matsuri (Bamboo Battle Festival)
There are three rounds of fights where the men start hitting each other with the bamboo sticks. Getting hit with a bamboo pole isn't pleasant and participants often walk away with bruises, cuts and welts. During the third round the poles are set on fire and there's an all out brawl against the two teams.
If the North wins it means there will be a good rice harvest for the coming year and if the South wins that's a signal that the price of rice will go up.
Onbashira Matsuri (Honored Pillars Festival)
The festival lasts a total of seven months and consists of two parts, Yamadashi and Satobiki. Yamadashi takes place during April and Satobiki takes place in May.
Yamadashi translates to "coming out of the mountains". This part of the festival involves citizens choosing sixteen 56-62 feet tall fir trees. The trees are cut down using specially crafted axes and are rode down the mountain by young men trying to prove their bravery. Once down the mountain the trees are adorned with traditional red and white Shinto decorations.
One month later during Satobiki the logs are brought to the four Shrines: Honmiya, Maemiya, Harumiya, and Akimiya where the are erected by hand using ropes. There's also singing and dancing while the logs are being raised.