All nine chapters from the "Episode 1: Escape from Wolfenstein" part of Wolfenstein 3D are hidden in the nine Nightmare levels in "Wolfenstein: The Old Blood". In each Wolfenstein: The Old Blood chapter, search for a secret room with an empty bed, a light, and a Wolfenstein 3D poster. Walk up to the pillow on the bed to display a "Nightmare" message. Hold [Action] to activate the bonus level, which is that level from the classic Wolfenstein 3D. After dying in the bonus level, you will wake up again in the bedroom you started the bonus level from. You can replay any Nightmare level. As soon as you wake up from a Nightmare, you will be able to go back to bed and enter the Nightmare again.

During the "Prologue" level you can find a poster featuring a scene from Wolfenstein 3D