Lucifer's Cage
This Cage was designed as a prison after Lucifer's rebellion. After being banished from Heaven for defying God, Lucifer decided to anger God by twisting a Human soul into the first demon. After this, God sent Michael to imprison Lucifer. This prison or cage, was locked with 600 Seals. Only 66 seals of the 600 had to be broken in order for Lucifer to be released. The interior of the Cage, according to Castiel, is heavily guarded even more so then when Dean was in Hell, suggesting an existence of other entities in the Cage or could simply mean that the Cage is complex and is difficult to travel through6.07 Family Matters This Cage seems to have multiple entrances or passageways. Unlike Angels, Fairies including The Leprechaun, can somehow get through "back doors" of prisons, and The Leprechaun claims that he can enter Lucifer's Cage6.09 Clap Your Hands If You Believe Despite the complexity of the Cage, Death travels through the Cage unaided and successfully retrieves Sam's soul and returns to Earth and places it inside Sam6.11 Appointment in Samarra
In 1972, Azazel possessed a priest at St. Mary's Convent, and killed eight nuns in the chapel. This enabled him to speak to the imprisoned Lucifer. Lucifer tells Azazel that Lilith is needed to break The 66 Seals that hold him captive in the Cage and that he needs to find a very special child.4.22 Lucifer Rising
This leads to the plan be Azazel to recruit select children, including Sam and the events that subsequently lead to the breaking of The 66 Seals.
In 2008 After Dean's return from Hell, Castiel reveals that Lilith is trying to break the seals that lock the Cage in order to free Lucifer. Dean later learns that the first seal was broken when he was in hell, and broke under torture and began torturing souls himself.
Sam continues clandestine missions with Ruby, developing his powers even though this involves drinking Demon Blood, believing that killing Lilith will avert the Cage being opened.
In 2009, Sam unknowingly releases Lucifer from his cage by killing Lilith at St. Mary's Convent. Lilith is revealed to have been the last of the 66 Seals.
As Sam and Dean attempt to find a way to stop Lucifer and the impending Apocalypse, Gabriel tells them that the Four Horsemen of the Apocalypse all own an individual rings that together form a key-like device that can reopen his Cage anywhere.
After collecting all the Rings, Sam comes up with a plan in which he will allow Lucifer to posses him, and then force him into the Cage. The initial attempt fails, but when Lucifer confronts Michael at Stull Cemetery, Dean activates the rings and as the cage opens, Sam manages to gain enough control to force Himself (and Lucifer) into the Cage. Michael (in possession of Adam) tries to stop him but is himself captured.
Raphael continues to work to find a way to open the Cage so that Michael can kill Lucifer.
Sam is subsequently released from the Cage by Crowley, but his soul and Adam's remained trapped in the Cage being tortured by Lucifer and Michael. Death agrees to retrieve Sam's soul, and return's it to his body, setting up a temporary 'wall' in Sam's mind to prevent the knowledge of what happened in the Cage from destroying him.
Where is the Cage?
The exact location of the Cage is unclear. It is obviously separate from the part of Hell where demons are produced, as it takes a great effort for Azazel to communicate with Lucifer. He eventually locates the Cage and communicates with Lucifer via the chapel of St. Mary's Convent. Later Dean is able to open the Cage via the Horseman's Rings in a deserted building and Sam uses them to open the Cage in Stull Cemetery. The fact that it can be entered from multiple locations suggests an existence in a different dimensional plane.
Sam refers to his time in the Cage as being "in Hell" 6.01 Exile On Main St. and Death says that he needs to go to Hell to retrieve Sam's soul.6.11 Appointment in Samarra
Sera Gamble described the Cage as being "at the bottom of the lowest depths of the ninth circle of the worst bit of Hell." Source.
See also:
Season 4
4.02 Are You There, God? It's Me, Dean Winchester
Castiel reveals to Dean Winchester that an angel by the name of Lucifer who is confined to a Cage, which will open when all of The 66 Seals break.
Dean: Why break the seal anyway?
Castiel: You think of the seals as locks on a door.
Castiel: Lucifer walks free.
Dean: Okay, last one opens, and?
– Dean, Castiel, 4.02 Are You There, God? It's Me, Dean Winchester
4.07 It's The Great Pumpkin, Sam Winchester
Castiel explains to Dean that if Lucifer ascends to from his Cage, hell and chaos will follow his presence on Earth. He later elaborates by saying that all of creation will literally experience hell if Lucifer roams Earth.
4.16 On The Head Of A Pin
And it is written that the first seal shall be broken when a righteous man sheds blood in Hell. As he breaks, so shall it break.
Castiel and Uriel ask Dean to torture Alastair to find out who is murdering angels. In the process, Alastair revels that it was Dean who broke the first seal of Lucifer's Cage.
4.22 Lucifer Rising
And it is written that the first demon shall be the last seal.
Ruby helps Sam find a demon who can reveal Lilith's location. In preparation for confronting Lilith, Ruby encourages Sam to drink the demon's blood (killing the woman it is possessing in the process). At St. Mary's Convent, Sam uses his powers to kill Lilith, only to have Ruby reveal that Lilith is actually the final Seal holding the Cage secure. Lilith’s blood forms a spiral circle in the middle of the chapel at St. Mary's Convent and the gates of Lucifer’s prison open and Lucifer is released into the world.
Season 5
5.19 Hammer Of The Gods
Without me, you got zero shot at killing Lucifer. Sorry. But... you can trap him. The cage you sprung Lucifer from, it's still down there, and maybe, just maybe, you can shove his ass back in. Not that it'll be easy. You got to get the cage open, trick my bro back into it, and oh yeah, avoid Michael and the God Squad. But hey - details, right? And here's the big secret, Lucifer himself doesn't even know. But the key to the cage, it's out there. Actually it's keys, plural, four keys. Well, four rings from the Horsemen. You get 'em all, you got the cage.
Sam and Dean try to kill Lucifer with the Colt but fail, and are desperate for a solution. 5.10 Abandon All Hope In a hidden message recorded on a Casa Erotica DVD, Gabriel reveals posthumously how Sam and Dean can trap Lucifer back in his cage. The keys to the cage are the rings worn by the Four Horsemen of the Apocalypse.
5.20 The Devil You Know
Crowley reveals he is aware of Sam and Dean's plan to get the Horsemen's Rings to trap Lucifer back in his cage thanks to his Magical Coin. He also tells them he wants to help them do it.
Sam comes up with a plan - he could consent to Lucifer's possession, and with much determination he could resist Satan’s for a brief moment; which would give him time to jump into Lucifer's cage with Lucifer inside of him. Bobby and Dean are both against the idea.
5.21 Two Minutes To Midnight
Sam and Dean get the final two rings after Castiel cuts off Pestilence's finger using Ruby's knife and Death gives his ring to Dean in exchange for his promise to do whatever it took to free him from Lucifer's control, ensuring that Sam would jump into the cage as soon as he consented to possession by Lucifer. Death also instructs Dean on how the rings work to open the cage, although the explanation is not shown in this episode. Dean is later shown working with all four rings on a table. They join together to form a triangular shape with War's ring in the center and the other three rings surrounding it. When Bobby asks him about Death teaching him how the rings work, Dean responds "Yeah, it's nuts."
5.22 Swan Song
Dean finally agrees to support Sam's plan though he has deep misgivings "Your hell is gonna make my tour look like Graceland."
Sam primes himself by drinking Demon Blood and then they confront Lucifer. Lucifer knows of their plan, but Sam says "yes" anyway. As Lucifer takes him over, Dean uses the ring and an incantation to open the "door" to the cage. However Lucifer is in control, and he easily closes it.
Later, in Stull Cemetery, Lucifer faces Michael who appears using Adam as a vessel. Lucifer tries to dissuade Michael from the fight, blaming their conflict on God, and suggesting they walk away. Michael counters that he must carry out God's orders, and that it's his destiny to kill Lucifer, who is evil. Just then Dean arrives in the Impala, Def Leppard's "Rock of Ages" blaring.
Dean tries to talk to Sam, inside Lucifer, but Michael tells him it's not his fight anymore. Castiel arrives and throws a Molotov cocktail made with Holy Oil at Michael, causing him to vanish temporarily. Lucifer turns and disintegrates Castiel, and then as Bobby shoots him, he snaps his neck.
Lucifer starts to beat Dean, taunting him, saying he will kill him slowly and make Sam feel it. Dean doesn't resist, just telling Sam he won't leave him. As he goes to land another blow, he glances at the Impala, and suddenly all Sam's memories of life with Dean rush at him, allowing Sam to take control over Lucifer. He tosses the Horsemen's Rings to the ground, recites the incantation to open the Cage. He and Dean look at each other one last time, but as Sam goes to throw himself in, Michael reappears. Michael tries to stop him, but Sam drags him into the chasm too, and it shuts. "
Season 6
6.01 Exile On Main St.
Sam reveals that he escaped the Cage soon after fumbling in it, more specifically being present for an entire year. Dean speculates that God may have brought him back. He remembers his time there, but when Dean asks, he doesn't want to talk about it.
6.03 The Third Man
Raphael intends to release Lucifer and Michael from the cage through unspecified means to complete the apocalyptic showdown.
6.06 You Can't Handle The Truth
Dean tells Bobby that Sam has been different ever since he was released from the Cage. He speculates that Sam may still be a Vessel for Lucifer but Castiel denies this, and says that if Lucifer was on Earth, he would've felt his presence.
6.07 Family Matters
Castiel determines that Sam has no Soul, and speculates that it was left behind in the Cage with Michael and Lucifer. He tells Dean the Cage is more well-guarded than Dean was when he was in Hell.
6.09 Clap Your Hands If You Believe
The Leprechaun is able to make deals with humans so that they may fulfill their wishes. He also seems to be very powerful, employing what he calls "real magic." He claims to be able to lift Sam's soul from Lucifer's Cage, and scoffs when Sam mentions that not even angels could accomplish that saying that fairies know about "Got a way of gettin' in back doors".
6.10 Caged Heat
Castiel tells Dean that Sam's soul, having been tortured by Lucifer for over a year, may be irrevocably damaged. Crowley also confirms this.
6.11 Appointment in Samarra
Dean has himself purposefully 'killed' under medical supervision, so he can plead with Death to rescue Sam and Adam from the Cage. Death agrees to rescue only one of them - and Dean chooses Sam. Death makes a wager with Dean, that if he will wear Death's ring for one day, and perform his duties, then Death will rescue Sam's soul. he tells Dean that he will be able to contain the part of Sam that will be damaged from his time trapped with Michael and Lucifer behind a 'wall' in Sam's mind, although he can't guarantee how long this will maintain. Although Dean fails to wear the ring for a day, Death agrees to retrieve Sam's soul, which he returns to Sam.
