A/N: This is influenced by the idea of Limbo from the film Inception, with the whole an-entire-lifetime-passing-in-a-day thing or whatever. I hope you enjoy it!

The Beginning

In the midst of the screaming and pain and darkness, there is a corner of Hell where nobody goes.

Let it never be said that demons enjoy the Pit, but there is a certain familiarity to treading thick, deep footsteps caked in blood and wondering how many souls gave up here; eyeing the broken fingernails embedded in dirt walls and wondering whose name that innocent being screamed on the way down. Demons don't want quiet. They don't want to be left alone.

Dean Winchester is sixty-seven years old.

Elsewhere, demons and broken souls are at play, wreaking havoc and causing pain, but here, there would be celebration. Today – if time in Hell can be measured in days – is the fortieth anniversary of the day that demons shrink to remember. The day that they call the Day of the Cold Fire. The day when bright white light tore the damned city into pieces, spiralling, slashing and slaughtering its way to Dean. Castiel was only starlight then.

He battled his way through blood and gore and tattered shadows of humanity to reach him – and then, unfortunately, discovered that to touch a soul in Hell is to find yourself grounded there indefinitely. After all, Lucifer couldn't make it too easy for his brothers and sisters to lay siege to Hell. However, if Castiel couldn't bring Dean to life, he could at least take the whips and knifes from his hands and keep him back from them.

Castiel built a wall, what seemed to be a hundred miles tall, built from light and rain-fresh valley air and the last whispering breaths of supernovas. As long as that wall stood, the bad things could not get in. And so forty years passed.

They grow old, both of them, like humans – together. Wrinkles cut deep trenches in their skin. Freckles, scars and then, much later, age spots all become familiar. The land they were given was bare and ugly, cutting a space out of the dirt where no space should have existed. The land they have now is bright. Beautiful.

The wood cabin is straight out of an old stereotyped romance; old wood that leans slightly to one side no matter how many times Dean fixes the tall front posts; butter-yellow trimming, dark green window-sashes, white mailbox, perpetually empty. Nothing planted in the soil here will ever grow, but Castiel likes the manual labour, the nurturing, the obsessive care. It reminds him of heaven. It reminds him of the job he was sent here to do.

Castiel makes sure that he is ever ready to do it, should the time finally arise. When they sit in silence on the long dock, side by side, arms brushing as they cast the line out again and again for fish that never come, Dean thinks about the things he'll say to Sammy when he finds him again, and Castiel plots Dean's body a hundred times in his head. The smattering of freckles, the break in his nose just below the ridge, the slopes of his shoulders. Narrow hips, endearingly curved legs, crooked toes. Castiel needs to remember it. He will need to put it all back together, piece by piece, on the way up.

They lie together for hours, mapping out the miles and millimetres of the other's skin – aging, beautiful pudge. They say nothing. There is nothing of the other they do not know. Dean has recounted the plot of the elementary school play that Sammy starred in, struggled to find the words for the overwhelming pride at Sam's high-pitched baby voice projecting a limerick through a dark room. Castiel has explained Byzantine politics of the old days and why the Hagia Sophia was so important. Dean now knows the names of every angel who has ever existed. Castiel can now air-guitar to every Led Zeppelin song ever written. He likes Stairway To Heaven, for obvious reasons. Early morning kisses and the midnight roll and jerk of hips together. They're not what they used to be but the territory's the same. They have shared every story, every joke, and every moment that they have lived so far. They have shared everything.

The Day of the Cold Fire is here again. The day is usually spent talking or remembering or simply being, but Castiel is nowhere to be seen. Dean climbs awkwardly to his feet, ignoring the sharp creak of badly-oiled joints, and finds him standing, slope-shouldered and tired, at the wall, gazing up.

"Cas," Dean calls hoarsely. "What're you doing out here, man?"

Castiel at first does not answer. He stares straight ahead, almost blindly, as though he has not noticed Dean's presence. Then he speaks, so softly that he is almost inaudible. "I've been preparing for this my whole life."

Shivers climb Dean's spine in slow, undulating jolts; fear creeps under his skin. "What's wrong?"

Only now does Castiel turn his head to face Dean, and his eyes are filled with a torment so intense and so anguished that Dean's throat chokes up tight and painful. They have always been so happy. This wall, this world... they've been sheltered. Everything is perfect, and yet Castiel seems a hairsbreadth from breaking.

"Cas?" Dean asks again, terrified of what the response may be.

Castiel swallows hard. He pauses. Lifts his chin a little, steels himself. "I have found the way out, Dean."

"The way out?" Dean can only echo dumbly.

"The way up." Castiel presses his lips into a thin line. "The way back – to your friends, your family. To Sam."

All at once the world seems as though it's grinding to a screeching, agonising halt and spinning wildly out of control. Dean is going home. He's going to see Sammy again. It has been forty years and he is finally, finally going home.

"Holy crap," he whispers, and for one hideous second he thinks he's actually going to well up. "Fuck. Jesus Christ, Cas. I mean. Shit." He can't come up with anything better than obscene expletives. He balls up a fist and presses his knuckles tight to his mouth in an attempt to control himself, but he splits. His grin is watery and every nerve ending is fizzing. "I can't believe it. Cas – we're going back! We're getting out! I mean... oh my god, Cas, you're gonna love Sammy. I swear to God, he's such a massive dork, he would love all your little stories. He would pee his pants for the shit you know... and, holy crap, you have to tell him that one story – you know, the one about that one time when Gabriel got in a massive feud with that Egyptian sun deity? Jesus, he would-"

"Dean," Castiel cuts in, sharp. "I am not coming with you."

Silence. There is no concept of time in Hell, so for all Dean can tell, his wounded confusion could stretch for days and weeks and months.

"What do you mean?" Dean at last asks. His voice is very small.

Castiel heaves a sigh that seems to drain all the strength from his body. He forces himself to continuing staring Dean straight in the eye, awkward and intent as always. "What you know of me cannot come with you," he says dully. "You understand, don't you... that none of this is real?"

There it is. The truth that Dean's been hiding from. He has known all along that when he returns to reality, these forty years will not have passed. Sam will not have aged. Dean's limbs will be young and supple again, and nothing will have changed. "I know that," Dean replies. "Of course, I know. But Cas, my soul-"

"-is unconscious," Castiel interrupts, almost shouting over Dean. There is a defiant, almost humiliated jut to the line of Castiel's jaw. He lifts a hand, flexes his fingers once, listening to the crack and pop of knuckles, and then presses his palm flat against the wall that he has so carefully constructed. "What do you think this wall is?" His voice is scratched raw, strangled. "This isn't to protect you from demons. This is protect you from yourself. You're still on the rack, Dean."

Dean just stares. He tries to imagine being back in that dark, bloody place. He can't even remember what Hell looks like. All that is left is this place in his head. The soft light, permanently dusky, in a land that casts no shadows. And Castiel.

"So what are you?" Dean demands, halfway between furious and devastated. "A figment of my imagination? An insanity hallucination, what?"

"I'm real. You aren't." Voice dropping back to a low rasp, Castiel's head snaps back to gaze at the wall. "When I withdraw from your head, this place will disappear. None of this will have ever existed and everything will go back to the way it was. I'll go back to my duties, having done my job, and you..." Castiel's voice snags. He licks his lips roughly, mechanically. "You will forget."

"I don't want to forget," Dean bursts out, sounding weak and childish. He can't even begin to wrap his head around it. "I can't forget. Cas – forty years!"

"Four months," Castiel corrects. "You've been dead four months. On the rack for three months. You started torturing two weeks ago and I found you yesterday." There is a harsh, apathetic bite to Castiel's words, as though he has resigned himself to his fate and is determined to slice himself open with it on the way out. He won't meet Dean's eyes now.

"Yesterday. Yesterday." Dean is aware that he should feel something – some gaping hollow inside his chest, some emotional collapse that takes his knees out from under him and leaves him a ragged mess on the floor. He doesn't. He stands rigid, mouth slack and stunned. "All this time, and... and what?"

There are suddenly hands on his face, curving to the shape of his jaw - thumbs skittering uncertainly across his cheekbones, fingers curling around the shell of his ear – and Dean knows without a doubt that no matter what Castiel says, this is real. This is as real as anything will ever be. "I will make you remember," Castiel says urgently, his brow crumpling. "I am real and I will find you and I will make you remember."

"Damn straight, Cas, you'd better," Dean says, trying for his most threatening voice. He remembers that he designed that voice for scaring the crap out of monsters and impressing his father; he remembers that more recently it's been used for telling off Castiel when he forgets to wash up after dinner, or when he cheats at cards because he can read Dean like a book after so many years, or when he pokes at Dean's expanding waistline and laughs and teases.

Dean doesn't want to go.

"So is this the end?" Dean asks shakily. They cling to each other like life-lines and both pretend they're not trembling.

"No, Dean." Castiel's eyes are hard and determined. He grips Dean's face tighter, fingernails digging half-moons into his skin, and leans like he's going to crush their mouths together, but doesn't. He abruptly lets go, hands drifting hopelessly, seeking purchase. One hand settles on Dean's left shoulder, squeezing once to reassure him. The other finds its way back to the wall, pressing flat against it. "It's only the beginning."

The light that had created the wall,, a light that had always seemed so warm and welcoming, is suddenly icy, searing, and brighter than anything Dean has ever seen. He isn't afraid though. He can feel Castiel with him. He's going home, and no matter where he goes or where he ends up, Castiel will find him.

The light overwhelms him. It is cold and it is screaming razor-sharp in his head so piercing that he thinks his head might explode. He can feel himself deteriorating. Everything is collapsing away around him, falling into dust, and the only thing that he can concretely pin himself to is the tight grip of a hand on his shoulder.

Dean closes his eyes in a garden.

ooo

Dean opens his eyes in a box.

There is an acute throbbing pain in his left shoulder and a high-pitched scream of ringing in his ears. He thinks of Sammy. He thinks of home. No matter what happens, he knows that he has to find his way back. With that in mind, and that fuelling him forwards, he beats his fingers bloody breaking through, and he climbs out into the sun.