Between 6th and 8th July, at Iriya Kishimojin Temple in Ueno, it was held the Iriya Asagao Ichi (Morning Glory Fair).
The schedule varies every year, so if you want to participate in 2010, you should inquire in advance. Last year, when I participated, the fair took place between 18th and 20th July. I knew that the fair attracts over 500,000 visitors, so to avoid the heat and congestion, I went in the morning.
I got off the train at the Iriya Station, and passing under the arcade announcing the event, I headed towards the temple, on Kototoi-dori.