Deep Underground is the second level of Area 51. It is a cutscene, narrated by Ethan Cole, and showing Bravo Team's descent into the base.
The elevator carrying Bravo Team descends as Ethan Cole narrates. U.S. military personnel are running around. Experimental projects are seen, as well as quarantined civilians. Infected soldiers attack a scientist and soldier. The military is then seen trying to contain the virus; soldiers throw a body into a burning pile, and a forklift knocks a helicopter off of a ledge, destroying it.