The levels in Duke Nukem I are divided into sequences known as episodes. The game contains three episodes, comprised of 10 levels each.
Episode 1 - Shrapnel City[]
Main Article: Shrapnel City in Duke Nukem I
Shrapnel City begins within the city. It ends with Dr. Proton escaping to the moon.
Episode 2 - Mission: Moonbase[]
Main Article: Mission: Moonbase
Mission: Moonbase begins at a base on the moon. It ends when Dr. Proton escapes to the future.
Episode 3 - Trapped in the Future![]
Main Article: Trapped in the Future!
Trapped in the Future! begins on Earth. It ends with Duke Nukem traveling through time to the future.