Secret 1: Window near the start
To access this secret place, you need a jetpack. If you do not have one from the previous levels, it can be obtained a little later in the level or straight from the beginning by blowing the sewer cover on the street in front of the police station and jumping into the hole. You will find yourself in a room with a couple of enemies and jetpack.
When you have jet pack, start at the very beginning of the level. Turn yourself towards the building on the left with black windowpanes. You will notice a graffiti on the wall - you need to fly into the window right above it. Inside the room you will find RPG, devastator, freezethrower, steroids and ammo for the expander.
Secret 2: Payphone
When you enter the police station, head to the right of the wrecked car. There you will notice a switch on a wooden wall. Flip it, then go across the room where a telephone was - now it lowered into the floor, unveiling a secret place with atomic health.
Secret 3: Interrogation room
In the same room where the jet pack could be found, which can also be accessed from inside the police station by going left from the car wreck then left again and down a ramp, open the gray swing door. You will find yourself behind a one-way mirror in an interrogation room with some recording equipment.
Notice the diagonal, darker wall in the room - it will open when you use the hidden switch on the recorder below two trip mines. Inside the small secret room you will find an atomic health.
Secret 4: Execution room
Behind one of the doors unlocked by the blue keycard, where the red key switch is located there will be a desk of J. McClain. Next to it will be a tall bookshelf - simply open it, it will rotate around and lead you to a secret ramp. Go down along it and you will find another secret room - execution room where firing squad used to do its work. There will be an atomic health and 3 chaingun cannons.
Secret 5: Hidden liquor stash
In the office with the Yellow Access Card on the desk, open the map on the back wall to find a secret compartment with liquor inside.
- In the room with the exit to Going Postal, there is a group of people hanging from a ceiling. This is a reference to the term "hung jury."
- In this level, the player come across office tables of famous action movie characters like J. McClane (from Die Hard movies), H. Callahan (from Dirty Harry movies) and Judge Dredd (a 2000AD comic book character from England). Duke would say their famous one liners for each respective characters.
- The level start out with a car crashing to the police station is actually a reference of the movie Terminator when the T-800 was about to start attacking the police station by ramming a car up the front desk. Player can hear gunshots and pigcops dying. Duke even hears the famous line "I'll be back", spoken by Arnold Schwarzenegger.
- The Wanted list in the station are actually photographs of the developers of Duke Nukem 3D. By examining it, Duke will say "Hmm, book 'em Danno", a reference to the popular TV show Hawaii Five-O.
- In one of the rooms there is a copying machine. By walking on it, Duke will copy his buttcheeks - a similar thing is possible in Duke Nukem Forever. The duke has a tattoo of " Lani <3 " on his buttcheeks, which is nickname of female voice actress Lani Minella.
- When activating the middle computer screen in the surveillance center, a duck will appear with an exclamation mark - possibly an urge for you to duck, because an Assault Commander will spawn behind you, launching a missile.
- Near Officer John McClane's desk there is a picture of the Unabomber, Theodore Kaczynski.
- At the front of the Judge's Stand, there is a symbol on there that is representative of the legal system of the United States. It should have "E pluribus unum" on it - which is the national motto of the United States; translated from Latin, it means "From many, one" or "Out of many, one." However in this game it says "E pluribus Nukem", which, roughly translated, means "From many, Duke."
- Go to the witness stand in the courtroom and Duke will say "So help me Duke", as opposed to "So help me God".
- In the interrogation room, there is a bloody glove on the table. This is likely a reference to the famous glove from the O.J. Simpson trial.
- The authorship of this level has been disputed. Richard "Levelord" Gray contributed to the level, but for reasons that are unclear, he was never officially credited for his work on it. The degree to which Gray and Randy Pitchford each deserves credit for the final design remains controversial. (See The Birth#Disputed authorship for more information.)