Attended a weekend long convention here. It's a very big venue with tons of rooms. For the convention we had a couple of rooms that could hold several hundred people and then some smaller rooms when we went to the different workshops. Each room you could have sound and projectors and the walls were magnetic as we used the walls to hold up big pieces of paper during brainstorming sessions. I have been here to for other events such as roller derby. There are several exhibitions halls for big events that can have thousands of people. Not too far from the Alliant Energy Center is the Veterans Coliseum which also holds a variety of events. There's a good chance you'll end up going to either of these places for a big event in Madison.