Friday, 28 July 2017
Comic Market - or Comiket, as this event is usually called - is the world’s biggest dojinshi (fanzine) fair and arguably Japan’s largest otaku gathering, visited by more than half a million people twice a year.
Here's a great video about the 28th edition (1985)
https://www.youtube.com/watch?v=cqtzepfEt-I where you can see how cosplayers looked back in the day.
You can find more information on dojinshi, Comiket, and other such events in the Odaiba chapter (p. 116-124) of the brand-new Tokyo Geek's Guide.