The keys we use every day are small metal objects with little grooves on them. Accustomed as we are to their use, it's hard to imagine something less tropeworthy than a humble key. Yet consider the symbolism of this tiny object- it opens that which is closed, changes barriers into passageways (or vice versa). A key in the wrong hands can be disastrous. And possession of a key can be a sign of authority and responsibility.
A Cool Key is one that is intended to reflect these values. It may simply be ornate and fancy, or it may have some special attributes that are unusual. The most common type is the Skeleton Key, which in addition to just being cool, is associated with the ability to open any lock for historical reasons: skeleton keys were used in antiquity to pass warded locks, which is why warded locks aren't very popular anymore. There are also master keys, which are designed to open any lock in a given set, allowing its possessor unlimited access to the household or area associated with the locks.
A Cool Key typically goes hand in hand (so to speak) with an equally elaborate lock or possibly a Cool Gate. In speculative settings, the key to a particular mechanism may not resemble a normal key at all.
- Sailor Pluto, guardian of the time gate in Sailor Moon, uses a giant key as her weapon. It's so big that when she stands on a floor with it, it reaches her neck.
- In Bobobo-Bo Bo-bobo, Hatenko uses the Fist Of Keys as a weapon to lock his opponents up.
- In Tengen Toppa Gurren Lagann, Simon's Core Drill not only activates his mini-mech, it also functions as a drill, albeit a very small one. He uses it to drill through Lordgenome at the end of the first Story Arc. In the Compilation Movie he also uses it to escape from a prison and climb a mech that is holding Nia hostage.
- The Millennium Key in Yu-Gi-Oh!. Shaped like a large ankh (cool-points there already) it had the power to "unlock" a person's soul chambers, allowing the user - Shadi - enter and explore the subject's memories and desires. Possibly even change them.
- The key to Superman's Fortress of Solitude is a huge thing that only he can lift; as a result, there's no need to hide it anywhere, he leaves it out in plain sight next to the door. It's also used as an aircraft path marker.
- In All-Star Superman, he replaces it with a small but super-dense key that supposedly weighs half a million tonnes. Whether or not he's exaggerating, only someone with his abilities can lift it.
- The Key to Hell that Lucifer passes to Dream of the Endless in Neil Gaiman's Sandman.
- The Magical Keys (seen above) from Locke and Key.
- The Justice League of America villain called The Key uses key-shaped gadgets.
- In Coraline, the key to opening the door to the other world has a button-shaped bow.
- The Keymaker in The Matrix Reloaded could make keys to open any door, or keys to make any door go to a particular destination.
- Not just doors. He could make a key to match any lock in the Matrix.
- The key to the elements chamber in The Fifth Element.
- James Butler Hickok Stark, aka Sandman Slim stole the key to The Room of Thirteen Doors, which is the only way to Earth from Hell (unless you're Lucifer himself). We don't know what the key looks like as Stark buried it in his body, but he doesn't need to actually fit it into a lock for it to work, either.
- In Garth Nix's Keys to the Kingdom books, there are seven keys, each signifying control over a part of the The House, and which each do different things (such as being able to transform into weapons or gloves).
- In Neverwhere, the key kept by the Black Friars is the main Plot Device. It the key to a gate to heaven as well as "to all reality", as the abbot says. The full limitations of this are not explained.
- The Key (note capitalisation) in The Lost Room has the ability to make any door (within certain specifications) lead into the Room, which has powers of its own. It's one of the most desired Objects in the show.
- The keys to the TARDIS look perfectly ordinary, but are given to companions as a sign that they've been fully accepted by the Doctor. More in line with the trope, they've been shown to glow when the TARDIS is active, and been retrofitted to make people ignore the person wearing them.
- The TARDIS key may look ordinary now (and in The Sixties), but back in The Seventies it looked like this, and in The Eighties like this.
- Doctor Who also had the Key to Time, which when assembled looked like a metal cube.
- The sonic screwdriver also often acts like a skeleton key.
- The Osterhagen Key is considered quite cool just because of what it does.
- In season 5 of Buffy the Vampire Slayer, a mystical key to alternate dimensions is transformed into human form, and the timeline is altered to place her into reality as Buffy's younger sister, Dawn.
- The Kaizoku Sentai Gokaiger have keys based on their many, many predecessors, allowing them to mimic their powers (basically, keys are to Gokaiger what cards are to Kamen Rider Decade).
- Dungeons & Dragons had at least 20 standard types of magical keys, each with its own powers.
- The "Skeleton Key" is a character template in BESM third edition; they have the power to open the portals between worlds.
- The Yatagarasu's Key in Ace Attorney Investigations. Not only is it very ornately designed, it also has a built-in knife blade!
- And the blade is also a key.
- Nethack: Rogues eventually get the Master Key of Thievery, an artifact that reduces physical damage by half and lets you control where you land after being teleported, in addition to being able to open any lock with 100% success. SLASH'EM adds three additional artifact keys (one for each alignment) that, while easier to get, only offer the 100% success on lock opening.
- Kingdom Hearts's Keyblades. Giant magical key-swords that can unlock any barrier and, as of the latest games, shape-shift into anything from a hovercraft to a cannon. Doesn't get much cooler than that.
- Zelda's Boss Keys or Big Keys usually have horns on the back, or horns as the teeth of the key. The Cel Shading games added an eye on the back of the key.
- The Legend of Zelda Twilight Princess' Boss Key has a more crystalline shape.
- The Legend of Zelda Skyward Sword's Boss Keys are 3-dimensional golden sculptures that have to be turned the right way before inserting them. Their shape is also thematically related to the dungeon they are found in; the one in the Ancient Cistern resembles the dungeon's central Buddha-like statue, while the Sand Ship's resembles a squid.
- In the NES games, Link can collect the Magical Key, an imposing lion-faced key in gold that can open infinite doors.
- Darksiders has a Beholder's Key that is basically a dagger. This is used to unlock "doors", which are actually forcefields with an eye in the middle. War takes the key and stabs it in the eye, lowering the force field.
- Wario Land 4: Keyzer, a ghost with a key for a nose.
- The old ZX Spectrum game Atic Atac had the Golden Key of ACG, a key with an ornate head and the letters ACG for the teeth (as a shout-out to the game's creators, Ashby Computers and Graphics). It was scattered around the game in three pieces; rebuilding it (in the right order) and using it to escape the castle was the whole goal of the game. (There were also regular keys for the four colour-coded locked doors.)
- A.B.A. of Guilty Gear uses a giant key that is also an axe as a weapon. Its name is Paracelsus, and it has googly eyes and a stitched-up mouth, and is larger than A.B.A. herself. Guilty Gear is that kind of game.
- Girl Genius had "the key" as MacGuffin with which one of Tarvek's relative fled other faction(s) of the family, both sides willing to murder anyone who stands on the way and take desperate risks up to messing with Corbettite Monk Order - which is something normally avoided even by madmen. Then there's a less intense, but wide search for it in Paris. When finally Agatha finds out what all the commotion is about, turns out that it's the key to a hidden lab of Van Rijn, "the greatest Spark of all time". Naturally, every Mad Scientist in Europa who have heard about it has the eyes glazed at the thought... even if they don't know where's the keyhole.
- In Red vs. Blue, Tucker's sword, a legendary binding artifact, has the second function of being the key to the hangar of a cool spaceship.
Church: So it's a sword. It just happens to function like a key in very specific situations.
Caboose: Or it's a key all the time, and when you stick it in people, it unlocks their death.
- In the Global Guardians PBEM Universe, the villainous Locksmith had a large, elaborate, and rather baroque-looking key that he uses to open any lock, and create "doorways"... dimensional tunnels from one location to another... by way of opening random door. When the heroes captured this "dimensional key", they discovered it was just a prop, and it was the man who had the power all along.
- The Lock Legion has the Key of Glorton.
- In Problem Sleuth, keys are sometimes weapons. The key is a pistol, the ring of keys is a machine gun, and the Megaton Key (a particularly cool key in its own right) is a set of brass knuckles.
- The SCP Foundation has SCP-005, a key that can open any lock in the world, provided the user can find and identify the lock.
- In the Adventure Time episode "The Enchiridion", the key to opening the gates to get the MacGuffin is literally the Gate Keeper, whose hat looks (and functions) just like a giant key.
- Avatar: The Last Airbender: The Air and Fire temples are both locked with mechanisms which can only opened by the appropriate bending discipline being used on the doors.
- The occupational badge (optionally) worn by US Air Force personnel in Intel career fields is a key superimposed over a globe.
- The Key to the City, an award occasionally bestowed on folks who do particularly good things for a city (such as being the Big Damn Heroes), is a tradition hearkening back to the days when cities were protected by walls with gates that they would lock at night to keep outsiders out. If you had a key to the city, you could come and go as you pleased.