You can unlock the following ghillie suits for your sniper classes by successfully completing the Ghillie in the Mist challenge:

• Arctic Camouflage - Get 50 one-shot kills using the sniper rifle to unlock the Arctic Camouflage Ghillie suit.
• Urban Camouflage - You will need to get a 100 one-shot kills using the sniper rifle to unlock the Urban Camouflage Ghillie suit.
• Desert Camouflage - You must get 200 one-shot kills using the sniper rifle to unlock the Desert Camouflage Ghillie suit.

You will unlock the museum once you have finished the campaign at any difficulty level. There is a red button in each exhibit hall which house the character models warning you to not press it. Press this button and all characters come to life and will try to kill you.