Kanamara Matsuri is unsurprisingly often referred to as “The Penis Festival.” It is infamous among foreign residents, but relatively unknown to the people of Kawasaki, the city which it is held in.
On first glance it seems like a celebration of genitalia (WARNING: DEPICTIONS OF MALE/FEMALE GENITALIA ARE BELOW. THIS IS CULTURAL AND NOT MEANT TO BE EXPLICITLY SEXUAL BUT SOME READERS MAY NOT WANT TO SEE…), but the event’s main goals are for prosperity, fertility, and as a protection against AIDS. The festival happens on the first Sunday of April. The closest station is Kawasaki Daishi.
Kanayama Shrine started out as a shrine for blacksmiths. One legend is that once there was a woman with vagina dentata (sharp-teeth in her vagina, caused by a demon) who kept unintentionally castrating men (ouch). She was desperate to cure herself, so she enlisted the help of a blacksmith who fashioned an iron phallus to break the teeth of the demon, effectively vanquishing it (a demon that apparently sometimes can hide out in your vagina. I am guessing periodic self-examination will prevent this from happening to you).
Prostitutes used to come to the shrine and pray for protection from sexually transmitted diseases. Others took the shrine to be a place for fertility and prosperity.
During Kanamara Matsuri some, um, very unique portable shrines make their way around town. The go around town to spread their luck.
After making the journey around town, the phalli come back home to the shrine area.
As you can see, the shrine area gets VERY CROWDED. You might want to get there early and leave early.
Would I recommend it? Yes, i would. I doubt there are many festivals like this out there. The other famous one is the Honen Matsuri in Nagoya.
There are a lot of interesting people who come out to enjoy the festival, so the atmosphere is really energized. After you see the festival you might want to walk over to Kawasaki Daishi. It is an impressive temple and has a street full of shops of sweets and souvenirs that leads up to the main worship hall.
Kawasaki Daishi HP: http://www.kawasakidaishi.com/english/cathedrals.html