Makuhari Messe is one of the biggest convention centers in Japan. Located in the East of Tokyo near Tokyo Disney Land, events like the Tokyo Game Show and Auto Salon are held here.
Up until the escalator accident that happened in Summer 2008, the Wonder Festival took place at Tokyo Big Sight. Neither Tokyo Big Sight, Kaiyodo or the escalator company wanted to take responsibility for the accident - which is why the Wonfes now always takes place at the Makuhari Messe.
Folks heading to Makuhari for any events (Chara Hobby up soon) should get off at Kaihin Makuhari station - map here.