The Easter Egg was later followed-up in Wolfenstein: The Old Blood where in every chapter all levels from first episode of Wolfenstein 3D can be played (See Nightmare (The Old Blood)) and been replaced in Wolfenstein II: The New Colossus by Wolfstone 3D where instead of just only one level or one episode the full modified version of Wolfenstein 3D can be played.
In the headquarters of the resistance movement, B.J Blazkowicz lies down on a mattress near a picture of himself at Castle Wolfenstein. He falls asleep and has a nightmare of his past experiences in circa 1945 (Operation: Eisenfaust).
He comments on his dream "Dreaming. Strange dreams. The killing never stops. Til I die."
The side mission background notes states: "Where am I? It's all a blurry haze. Think I need to get out of this place."
Earlier back in 1946, he also remembered a more complete version of the events including up to his defeating Hans Grösse at Castle Wolfenstein.
- A The Wolfenstein (2009) graphic novels also included Wolfenstein 3-D as part of the series history in the same timeline. It put Wolfenstein 3-D as the end of the Third Reich (either before 1943 (RTCW materials) or during 1945 (Wolfenstein 3D Classic) and the rise of the New Reich/Fourth Reich in the late 1945-1946 period (placing 2009 game in an alternate WW2 history c. 1945/1946). The Spear of Destiny hintbooks may also suggest that Wolfenstein 3D took place at an earlier point in the timeline between 1942-1944, representing one of the many early 'attempts' on Hitler's life, before his actual 'suicide' in 1945. Due to the nature of there being several possible dates given for Wolfenstein 3D (from alternate endings given in different versions of the game), and at least two attempts on Hitler by B.J. himself (Original Encounter/Wolfenstein 3D's original missions - "3rd Encounter" - its impossible to know how Machine Games has 'interpreted' the events)
- Several secret locations are in the level. Also there is a hidden exit although both exits lead the player to the same location.
- Wolfenstein: The New Order includes a somewhat similarly altered history (although no evidence if it was directly inspired by the graphic novels) in which the battles with Deathshead continue into 1946, and the Nazis ultimately win the war by the late 1948, and Blazkowicz wakes up from a coma and begins fighting the "New Order".
- Following the "nightmare", the end of the level contains a waking up animation, as Blazkowicz wakes up from the mattress.
- Near the bed are photographs, propaganda, and other documents on the wall. One of these pictures depicts B.J. Blazkowicz escaping Castle Wolfenstein just as in the nightmare. This is actually the background art of the original Wolfenstein 3D title screen.
- Enemy comments have subtitles just like regular enemies in the game (though translated into English from German).
- There are no checkpoint in this secret level, if B.J. is killed, he will have to restart at the beginning of the HQ mission. However, completion of this level is not necessary to progress the story.
- The last secret near the secret level exit, has sardine cans which spell out the letters MG (a reference to Machine Games). There are three more cans below it placed in a slanting formation.
- Wolfenstein 3D can be seen on an officer's computer on the moon, and a poster above the bed in the Tools room.
- When Gamespot asked Activision if Robohitler would be in Wolfenstein: The New Order, they were told that he was already defeated in Wolfenstein 3D (but still possibly alive). It was suggested to them that events of Wolfenstein 3D were still canon. This may have been in part a nod to this particular easter egg (and expanded Nightmare series of levels in The Old Blood).
- The Assault Rifle 1946 can be found in one of the first secret areas.
- Wolfenstein: The Old Blood has nine Nightmare levels hidden throughout the game, each based on a classic Wolfenstein levels of the first Episode. This also represents a continuation of B.J.'s memories and an easter egg, an a nod the original wolfenstein series made in the New Order. They lead up to the defeat of Hans Grosse, and escape from Castle Wolfenstein. They load up showing new B.J.'s face pixelize into old B.J.'s face (and vice versa if you die/wake up). All the secret beds also have a poster or postcard with image from Wolfenstein 3D pointing out a location where the nightmare is accessable (some also include a bottle of wine with the Wolfenstein Logo and old B.J.'s face on it). The levels are slightly more accurate than the Nightmare! version in New Order in that they include more enemy variety including dogs, lieutenants and others. The secret exit at the end of the Alps Nightmare level acts like a functional elevator and rises into the secret level from Episode 1 from Wolfenstein 3D. All of the secret nightmare levels include functioning mapping mode.
- Defeating the last of the nightmare missions in Old Blood nets the Die, Grösse, die! Trophy.
- Old silver bars (dated 1928) are a treasure found in the nightmare levels in The Old Blood. They more or less take the place of various treasures found in the original Wolfenstein 3D. Finding all the silver bars unlocks character background information for the Nightmare levels in the Characters section of the Extras menu.
- The weapons in the Nightmare levels of Old Blood include the silenced pistol, knife, and the 1946 version of the assault rifle, and dual wielded weapons. Though this is less likely intended to be a dating reference for the dream, but rather just reuse of available programmed weapons, rather than include new weapons specifically for the dream sequence. This makes the weapons a bit less accurate portrayal to the weapons found in the original versions of Episode 1, which had the more noisy pistol, and only ability to use one weapon at a time.