A classic game played to illustrate how we put up artificial barriers between individuals/teams at work, which leads to competition rather than co-operation, and is damaging to the customer/organisation.
The game lasts from 30-45 minutes (depends how tightly you manage the time) and you will need a separate room or area for half the group.
If you have a large group (more than 16) the Black-White Game may be better. It works the same way and has exactly the same learning points, but you split the group into 4 rather than 2. Obviously, you need 4 areas for delegates to work in, and it may take a little longer to run.