Hands down the bridge-keeper encounter in Fallout 2. A classic Monty Python Quest for the Holly Grail reference!

Thank you for this idea! Very interesting. I hardly post anything and I have been watching this thread for a long time now, so far it seems no one mentioned my favorite video game secret/easter egg. I did not check the social media comments.

My favorite video game secret/easter egg appears in SWAT 3: Tactical Game of the Year Edition.

It is also very well hidden, most players seem to complete the mission without discovering. I have searched for videos online showing this egg, and they do not seem to be complete at all.

Basically, it is a "The Matrix" reference, but it goes beyond usual easter eggs, it is also well made.

There is a subway mission where they have recreated the "The Matrix Smith Subway Fight Scene" featuring Agent Smith! Please search for this video and compare the screenshots to see how accurate it looks.

Bottom line: If you watched any Matrix movie, you probably noticed that the Matrix agents send the SWAT to hunt down the "good guys".
Therefore, it is not only funny and interesting; it makes you think about the possibility that you were being used as well... until you pick up the phone and learn the secret!
It switches the scene to a whole new perspective that leaves the player pondering which team should open each door like never before: red or blue?

Instructions: The mission at 12th & Figueroa, a Rapid Deployment on Newton; you can enter it instantly without a career right after installing the game.

As an officer, you are not supposed to shoot civilian NPCs, only threatening NPCs.
At first, there is often a civilian who runs towards the platform on the other side of the road, if you chase them, you will find a pay phone cabin and a homeless laying down.

This pay phone eventually starts ringing (may take up to several minutes to happen). You only have a few seconds to answer the phone. If you proceed, the homeless is replaced by Agent Smith, who gets up and starts shooting at you (and the phone cabin).

Besides that, there is a hidden passage behind a cracked wall. Behind the wall there is a recorder. If you touch the recorder, it self-destructs and you are transported to a room with green letters with more hostile agents. On the other building, there is also a dangerous black cat (deja vu reference) that can push you off a ledge.

Notes: I took the screenshots from the GOG version. It took several attempts to get them right. I joined them into a single picture to cope with size limit, I still have many more originals. They are supposed to be darker: I increased brightness in the game options because it was too hard to see all details in the default setting.

Regardless of the contest, I really hope to encourage someone else to try Swat 3, it is a great game. Swat 3 includes many interesting educational information about safety and procedures that are not present in Swat 4 (and yet, both are awesome and have many other easter eggs). Thank you SparkyDPitbull for mentioning Swat 4! And special thanks to RenanSPH for the co-op moments that allowed me to discover these secrets. In summary: Yes GOG, please feel free to use this to advertise the Police Quest/Swat Series any time.

If you find trouble running Swat 3 on recent Windows versions or WINE, try running swat.exe with the -nointro parameter.

Edit: screenshot re-upload and small fix. Later moved the bottom line with something I forgot earlier... Added thanks.

I think one of the more wierd easter eggs that I have ever experienced was one that stemmed fro Call of Duty's debut on home consoles, "Finest Hour". It was in a sewer based level that involved the player breaking a barrier with grenades, opening a passage which lead to a room of German soldiers and a Russian ally and protagonist from several levels prior dancing crazily. People were making on dance movements that involved flailing arms and doing spinning handstands, all facing eachother in a circle beside a fire. It did not matter that Russian had previously been seriously injured. Of course the dancing was topped off by beatboxing.

In Mike Tyson's Punch Out for the NES, if you put in Nintendo's customer service number for the passcode, you got a busy signal. Some programmer had a sense of humor. Haha!

My favorite easter egg is the Normandy In no man's sky.

The Batman/Batcave Easter Egg in King's Quest 2. I was a little afraid to enter the cave of the old hag/witch, so I backed out to another screen, then changed my mind and went back to the cave entrance screen, then said, "Nope, not yet" and went down to the other screen, then said, "ahh to heck with it, I'm going for it" went back up to the cave screen and it happened! I suddenly heard a car start, then the old Batman theme music began, and the batmobile came driving out of the old hag's/witch's cave, back and forth several times, as if Batman had fogotten something and would return to the cave, then head back out again. To top it off, in the final scene at the wedding ceremony, guess who's present as a guest? Yup...Batman!

I don't know if they qualify for easter eggs, but in Remedy's Max Payne games you will get some kind of reward when you complete the game on hard setting.

Otherwise one of the most unbelievable easter eggs is in Day of the Tentacle, where the entire Maniac Mansion game is included.

Well i personaly think that finding the climbing rout for some of the viewpoints in of itself deserv to be an easter egg.
If that doesn't count my answer has to be the bromstick and other every day items that you can potentionaly use as an improvised wapon is a definitly fun one.

Fallout 2 where you have the special encounter "Guardian of Forever" allowing you to go back in time to Vault 13 and break the 'water chip', the reason for the vault dweller leaving the vault in Fallout 1, and the "Guardian of Forever" happebns to be a Star Trek reference as well :)

I see that we think alike. :-)

Super Punch out had a secret two player mode where someone could play as the other fighters. It was not discovered until last month, 28 years later!

https://www.ign.com/articles/super-punch-out-secret-two-player-mode-discovered

In ff7 when cloud is recovering in mideel the stuff he says is a reference to the lyrics in a xenogears song.

My favorite easter egg has to be all the Calendar Man stuff in Arkham City, visiting him on the specific dates every month to hear the full story he tells and then manually setting the clock back to Rocksteady's founding to hear him reference their start.

Probably heads of developers in Serious Sam series, funny and annoying. Give yourself to the slaughter for players - guys from Croteam are not only inventive, but also with a sense of humor.

I think the most notable easter egg I enjoyed was the easter egg connection between The Witcher 3 and Cyberpunk 2077

<--SPOILER ALERT-->

Ciri describes a world she hid in to escape the titular Hunt, she says "People there had metal in their heads, waged war from a distance, using things similar to megascopes. And there were no horses, everyone had their own flying ships instead.".... Now it doesn't appear as an easter egg at first, but 5 years later and we get Cyberpunk 2077... The creators of The Witcher 3 and Cyberpunk 2077 are one in the same. This is an interesting "Easter egg" because it took 5 years for it to start to gain awareness among the gaming community, and I personally find it interesting that this is one of those "Stumbled across a random but cool coincidental easter egg" sorta moments, and that's what gets me.