This is a technique for a large number of people (max I've done successfully is 50) to have a good discussion.
Put five (or so) chairs in a circle in the middle of the room, and all the rest concentrically around it.
One of the chairs must remain empty.
Only someone in one of the chairs may speak.
Anyone may sit down in the empty chair.
You will need some light facilitation if people don't get the rules immediately.
You MUST have a good topic, otherwise people just come into the circle to air their views, not to take part in a discussion. This means a topic where there are clear conflicting views.
About an hour is usually enough.
See FishBowl, ParkBenchPanel