Every video game contains hidden secrets and Easter eggs. As a player, finding them is never a small feat. Even if they are easy to spot, it always feels like you've discovered something special that you were never intended to see.

Sometimes developers put these secrets in places that are hard to reach, but most Easter eggs are found pretty quickly — especially nowadays, when the ins-and-outs of every video game can be learned with a quick internet search. These secrets, though? These are some of the rarest, most well-hidden secrets in the history of video games.

It has taken gamers decades to find some of these treasures. Not only are these Easter eggs super obscure, but many of them were never meant to be found by the player. Whether it's a well-hidden reference, a secret item, a shocking glitch, or a newly-explorable area, these hidden gems were so hard to find that some developers thought that they would never be seen by anyone! Have no fear, completists, because we're here to help.

For this list, we've collected some of the most obscure long-standing video game secrets in the entire world. The list spans generations in technology, and sometimes the secrets are so complex that they lead outside of the game world itself. Seriously, some of these are so crazy that you'll wonder how anybody ever thought to look for them in the first place.

Think you've found them all? Here are 20 Hidden Things In Video Games That Weren't Found For Years.

Quincy Sharp's Office (Batman: Arkham Asylum)

Arkham Asylum Secret Plans Easter Egg

Arkham Asylum is chock-full of Easter eggs and references. If you're a DC comics fan or a Batman aficionado, these can be quite easy to catch. However, this one is so hard to find that players may never have never found it had the development studio not leaked its existence nearly three years later.

In Warden Sharp's office, there's an unmarked wall.

It's totally inconspicuous and Batman's detective vision (which usually lets the player see through breakable walls) will it as any other ordinary wall. However, detonating explosives on the wall will unveil a hidden room. In this room is a number of references to Arkham Asylum's sequel, Arkham City.

Rocksteady Studios teased Arkham City years before its release. Because nobody found the room, nobody noticed.

Happy Birthday Lauren! (Halo 3)

Master Chief in Halo 3 trailer

The Halo series is infamous for its collectable secret skulls that unlock gameplay modifiers, but this secret was a little bit different. Bungie coder Adrien Perez wanted to leave a message for his wife Lauren in his company's newest project.

Starting a single-player level in Halo 3 and holding down the thumbsticks will reveal "Happy Birthday Lauren!" in the loading screen's ring. How sweet! This can only be seen on December 25th of any given year, so either break out your copy of Halo 3 next Christmas or set your console's date and time accordingly.

It's a cute little Easter egg that went unnoticed for many years, but let's hope that Lauren really was the first person to discover it!

Splinter Seals (Splinter Cell: Double Agent)

Splinter Cell Double Agent

Tom Clancy's Splinter Cell games are known for their gritty military action, so players were pretty shocked when they stumbled upon a secret set of quests involving space-travelling seals wearing party hats.

Throughout the game, the player must collect a variety of items for the seals. 

They reward the player with information about the next seal's location, as rescuing them all will return them to their home. Rinse and repeat until you've found them all, and their princess will express her gratitude.

Splinter Cell: Double Agent is an especially dark entry in the franchise too, as Sam Fisher has to go undercover in a terrorist organization in order to shut them down. A noble endeavor — perhaps just as noble as getting Muffin, Cookie, Vanilla, Buddy, and Pepperoni back to their home planet.

Zelda Chris Houlihan Room

If you ever stumbled upon this odd treasure room in A Link to the Past, you were probably momentarily confused before you were overwhelmed with joy.

The Chris Houlihan Room is a "secret" location named after the winner of a Nintendo Power magazine contest, with the prize being the winner's name featured in a future Nintendo release.

The room appears during a glitch — when the game doesn't know where to spawn Link, it defaults his position to this room. There are several ways of triggering the glitch, but each will end up in Chris Houlihan's rupee stash.

Unfortunately for Mr. Houlihan, his name only appears in the original game, as the text is replaced in the Game Boy Advance version.

The Man In The Green Jacket (Resident Evil 4)

Leon S. Kennedy holding a handgun while zombies stalk him in Resident Evil 4.

This might be one of the spookiest things in Resident Evil 4 and it took over 12 years to find.

Right after the helicopter crash sequence, a mysterious figure can be seen in the background out of the game's playable area. The game's color grade is so dark and dim that it is nearly impossible to make him out, but freeing the camera enables for a closeup that still doesn't explain much.

Way off in the distance is a blurry, 2D figure of a man in a green jacket.

He's smiling and holding up peace signs (we think), and there's really no reason why he should be standing here. This is likely the developers playing some kind of inside joke, but the man remains a mystery.

The Impossible Coin (Super Mario 64)

Super Mario 64 Impossible Coin

It's common practice among video game completists to prefer platforming games littered with collectables. Progress can easily be tracked along the way as they grab each item, so it's always clear how far any given player is from completing the game with a 100 percent rating. However, Super Mario 64 has a coin that nobody has ever collected — without cheating, of course.

This slope of coins on Tiny Huge Island is supposed to be a row of five, not four. Because of a small programming mishap, the fifth coin that should appear at top of the slope actually spawns underground, thus making it completely inaccessible.

This hidden coin has made players grit their teeth for decades. It's so close we can taste it!

Beating The End (Metal Gear Solid 3: Snake Eater)

Metal Gear Solid 3 Snake Eater The End Boss

Solid Snake has dealt with some tough enemy encounters, but none of them are as tough as The End-- or as easy, if you're aware of this secret.

The End is a veteran sniper and one of the game's hardest bosses.  The battle might last a while, but players who took a break from the game for over a year were gifted with an odd surprise.

Waiting at least a year to finish the boss battle will result in nature taking its course. The End's old age will catch up with him.

Snake won't have to lift a finger.

Fast-forwarding the console's system date one year yields the same result, if you're in a hurry. Careful, though, as shorter breaks from the game may result in Snake getting captured by enemy forces.

The Sarcastic Announcer (Wave Race: Blue Coast)

Wave Race Blue Coast GCN Gameplay

This jet ski racing title on the Nintendo Gamecube has an Easter egg that took 10 years to find. Was it worth it? Probably not — unless you really like getting ive-aggressively insulted about the way you play Wave Race.

Going to the game's options menu and inputting a secret code makes a very bizarre change to the in-game narrator. Using the code and starting a race will reveal that the upbeat announcer is suddenly feeling a lot more grouchy and sarcastic. His words of encouragement suddenly turn into dry quips and insults, and his voice becomes bored and monotone.

You'll suddenly feel a lot more insecure about playing a breezy racing game, but it's a cool secret nonetheless.

Big Foot VS. Teen Wolf (Grand Theft Auto V)

Grand Theft Auto V Big Foot Teen Wolf Secret

A few years ago, Grand Theft Auto V players found mysterious peyote plants scattered across Los Santos that would turn avatars into a Sasquatch when collected. Yes, really.

This seemed like the Easter egg at first, but it led to something much weirder. As dedicated community of players combed through the game's code, they realized that the plants were leading them somewhere.

It turned out to be more of a literal hunt than a scavenger hunt, as eventually players stumbled upon the Beast, a Michael J. Fox-looking werewolf that attacks on sight.

Beating the Beast rewards the player with his Teen Wolf inspired costume. Seriously, what else could possibly be hidden in this game?

Calendar Man's Monologue

Calendar Man Arkham City

Arkham Asylum teased the events of Arkham City, but Arkham City managed to one-up its predecessor with an even more cryptic secret. Visiting Calendar Man on different days will result in different conversations between him and Batman. However, setting your console's date to December 13, 2004 will reveal new dialogue.

Calendar Man will reference the end of the following game, Arkham Knight, and promise Batman that he'll be present for his demise. The ending of Arkham Knight does indeed feature Calendar Man, and the date corresponds to the founding of the game's development studio, Rocksteady.

This secret was only discovered three years after release when a mysterious video appeared online by er "JG Jour" — a french twist on Calendar Man's identity, Julian Gregory Day. Did Rocksteady leak this secret too?