I think the Banjo-Kazooie cheats fit the bill.
In one early level there's a chamber with a puzzle in it:
The objective of the puzzle is simply to spell out BANJO-KAZOOIE on the floor by walking to each letter and stomping it. This takes a little while because 'typing' isn't a quick process.
You can, however, enter other things there.
There's the cheats actually shown to you in-game that I'm not counting (because, well, they're explicitly shown to you in-game. And I'm fairly sure they can't be used until you've seen them - they're not actual cheats, even though they're presented as such, just upgrades under the theme of cheating)
REDFEATHERS - doubles limit of red feathers
BLUEEGGS - doubles limit of blue eggs
GOLDFEATHERS - doubles limit of gold feathers
...and there's some bonus unlockables that are also shown to you in-game
BOTTLESBONUSONE - Makes Banjo's head large.
BOTTLESBONUSTWO - Makes Banjo's hands and feet large.
BOTTLESBONUSTHREE - Makes Kazooie's head and wings large.
BOTTLESBONUSFOUR - Makes Banjo's head small and his torso long and sausage-like.
BOTTLESBONUSFIVE - Makes Banjo's head small, his hands and feet large, and gives him a sausage body.
BIGBOTTLESBONUS - Makes Banjo's head, hands, and feet, and Kazooie's head and wings, large.
WISHYWASHYBANJO - Turns Banjo into Washing Machine Banjo.
NOBONUS - Returns Banjo and Kazooie to normal.
But the real cheats... First, note the length of those. Now, imagine your reaction on seeing *these* claimed to also work:
CHEAT NOW YOU CAN SEE A NICE ICE KEY WHICH YOU CAN HAVE FOR FREE - Ice wall blocking Ice Key in Freezeezy Peak disappears.
CHEAT OUT OF THE SEA IT RISES TO REVEAL MORE SECRET PRIZES - Sharkfood Island in Treasure Trove Cove rises from the sea, allowing collection of the Pink Mystery Egg.
CHEAT A DESERT DOOR OPENS WIDE ANCIENT SECRETS WAIT INSIDE - Door in Gobi's Valley vanishes, allowing collection of the Blue Mystery Egg.
CHEAT DONT YOU GO AND TELL HER ABOUT THE SECRET IN HER CELLAR - Metallic crate in Mad Monster Mansion's cellar opens, allowing collection of the Cyan Mystery Egg.
CHEAT AMIDST THE HAUNTED GLOOM A SECRET IN THE BATHROOM - Green Mystery Egg appears on top of Loggo in Mad Monster Mansion's bathroom.
CHEAT THIS SECRET YOULL BE GRABBIN IN THE CAPTAINS CABIN - Red Mystery Egg appears on top of the bed in Rusty Bucket Bay's ships's bedroom.
CHEAT NOW BANJO WILL BE ABLE TO SEE IT ON NABNUTS TABLE - Yellow Mystery Egg appears in Nabnut's House in Click Clock Wood (winter).
CHEAT BANJO BEGS FOR PLENTY OF EGGS - Infinite Blue Eggs.
CHEAT NOW YOU CAN FLY HIGH IN THE SKY - Infinite Red Feathers.
CHEAT A GOLDEN GLOW TO PROTECT BANJO - Infinite Golden Feathers.
CHEAT GIVE THE BEAR LOTS OF AIR - Infinite air while swimming.
CHEAT LOTS OF GOES WITH MANY BANJOS - Infinite lives.
CHEAT DONT BE A DUMBO GO SEE MUMBO - Instant 99 Mumbo Tokens. Will remain even after quitting.
CHEAT AN ENERGY BAR TO GET YOU FAR - Instantly get eight honeycomb containers.
CHEAT THIS COMES IN HANDY TO OPEN SOME WHERE SANDY - Open Treasure Trove Cove.
CHEAT THERES NOWHERE DANKER THAN IN WITH CLANKER - Open Clanker's Cavern.
CHEAT NOW INTO THE SWAMP YOU CAN STOMP - Open Bubblegloop Swamp.
CHEAT GOBIS JIGGY IS NOW DONE TREK ON IN AND GET SOME SUN - Open Gobi's Valley.
CHEAT THE JIGGYS DONE SO OFF YOU GO INTO FREEZEEZY PEAK AND ITS SNOW - Open Freezeezy Peak.
CHEAT THE JIGGYS NOW MADE WHOLE INTO THE MANSION YOU CAN STROLL - Open Mad Monster Mansion.
CHEAT WHY NOT TAKE A TRIP INSIDE GRUNTYS RUSTY SHIP - Open Rusty Bucket Bay.
CHEAT THIS ONES GOOD AS YOU CAN ENTER THE WOOD - Open Click Clock Wood.
CHEAT THESE GO RIGHT ON THROUGH NOTE DOOR TWO - Open the 180 Note Door.
CHEAT NOTE DOOR THREE GET IN FOR FREE - Open the 260 Note Door.
CHEAT TAKE A TOUR THROUGH NOTE DOOR FOUR - Open the 350 Note Door.
CHEAT USE THIS CHEAT NOTE DOOR FIVE IS BEAT - Open the 450 Note Door.
CHEAT THIS TRICKS USED TO OPEN NOTE DOOR SIX - Open the 640 Note Door.
CHEAT THE SEVENTH NOTE DOOR IS NOW NO MORE - Open the 765 Note Door.
CHEAT YOULL CEASE TO GRIPE WHEN UP GOES A PIPE - Raises the big pipe near Clanker's Cavern.
CHEAT BOTH PIPES ARE THERE TO CLANKERS LAIR - Raises the two pipes near Clanker's Cavern.
CHEAT UP YOU GO WITHOUT A HITCH UP TO THE WATER LEVEL SWITCH - Raises the water level near Rusty Bucket Bay.
CHEAT THEY CAUSE TROUBLE BUT NOW THEYRE RUBBLE - Removes all breakable walls.
CHEAT YOU WONT HAVE TO WAIT NOW THERES NO CRYPT GATE - Removes the crypt gate near Mad Monster Mansion.
CHEAT DONT DESPAIR THE TREE JIGGY PODIUM IS THERE - Reveals the Jiggy pad for the Click Clock Wood puzzle.
CHEAT THE GRILLE GOES BOOM TO THE SHIP PICTURE ROOM - Removes the grille blocking the Rusty Bucket Bay puzzle.
CHEAT SHES AN UGLY BAT SO REMOVE HER GRILLE AND HAT - Same effect as the Bubblegloop Swamp Witch Switch.
CHEAT GRUNTY WILL CRY NOW YOUVE SMASHED HER EYE - Breaks the eye of the Grunty statue.
CHEAT THIS SHOULD GET RID OF THE CRYPT COFFIN LID - Breaks the lid of the crypt coffin.
CHEAT ITS YOUR LUCKY DAY AS THE ICEBALL MELTS AWAY - Breaks the ice ball blocking the pipe to Cheato near the Freezeezy Peak puzzle.
CHEAT WEBS STOP YOUR PLAY SO TAKE THEM AWAY - Removes all webs.
CHEAT YOULL BE GLAD TO SEE THE SHOCK JUMP PAD - Makes the Shock Jump Pad usable.
CHEAT YOU WONT BE SAD NOW YOU CAN USE THE FLY PAD - Makes the Flight Pad usable.
They do, indeed, work.