The Museum Call of Duty: MW2 Guide

After finishing the single player campaign and watching the end credits, a bonus mission will be unlocked - The Museum. You can take a look round two rooms filled with characters from the game #1. Additionally the weapons from the game are all placed in display cases #2.

The mission itself doesn't have a real objective. However if you do press the red button on the desk #1, all the characters will come to life and start shooting at you #2. Eliminating them is quite challenge, despite the amount of weapons on your disposal. Each room has a separate button used to activate the characters, so at least you can be sure you won't be attacked from behind.