Bon Odori - an event carried out during the Buddhist festival of the dead, which honors the spirits of one's deceased ancestors. People gather around a wooden tower, and dance in unison to local folk songs and enka classics.
The Marunouchi Ondo Bon Dance Festival [丸の内音頭大盆踊り大会] in Hibiya Park took place the other day and you can see what went on in the festivities that day.
I love traditional Japan but I hear that some folks prefer the modern. I enjoy both though - how about you?
Get off at Hibiya station on the Hibiya line and you'll be at the park.