Sam is out for beer and pizza when it happens.
Dean sees his breath first. Starts hunting a non-existent ghost, wastes time fetching salt rounds and iron before he slips on the frost creeping across the floor.
It spreads beneath him, freezes his jeans to the hardwood. "Shit." Fumbles for his phone, fingers already stiffening with cold. "Yeah, Sam? Where are you? Cos we got a problem."
Icicles start to form in the doorway.
"The bunker's turning into a freezer." Holds the phone with his chin as he peels himself off the floor. "No, an actual freezer. Meet you outside."
Dean pulls sleeves down over his hands. The railing is too cold to touch. The stairs are covered in ice, and his boots slide as he climbs. It slows his ascent and every breath he takes sears his lungs and chills him to the bone.
He's reminded of frozen bodies left behind on Everest.
The door seals are crusted with thick frost. Ice crunches as he turns the handle.
The door doesn't budge. He pounds on it, kicks it. It doesn't move.
"Sam," he yells. Wastes energy he cannot spare beating at the door. Screams for his brother until he's hoarse.
Dean backs away, stumbles back down the stairs. Makes it to his room and pulls on every item of clothing he can find. There's a black beanie shoved deep in the bottom of his duffle, part of his B&E outfit, and he pulls it on.
His phone rings. The screen cracks when he pulls it out of his pocket. "Sam," he says. His teeth chatter together so hard he can barely speak. "Door's frozen shut."
He listens to Sam's frantic instructions. Gathers the gear he needs, makes his way, slowly, joints stiff, back to the stairs.
He starts the climb again. Slips and falls to his knees halfway up. They'll call him Brown Boots or something, when they pass his frozen corpse on the way to the summit.
There's a banging from above. A pounding, a ringing. "Dean!" Sam's voice is muffled through the cold, and ice, and thick steel.
Dean pulls himself up. Inches to the top. He can't feel his fingers, or his toes. Pulls handfuls of salt out of his pockets, rubs it around the edges of the door. Squirts lighter fluid over it all.
Strikes a match. It fizzes and dies. The next one breaks.
Finally, he gets a flame. He shakes as he touches it to the door, watches as fire rings the doorway, burning away the flammable liquid, then winks out.
He falls back, slides down the railing. He's cold, and tired, and he closes his eyes, just for a moment.
Dean wakes with his fingers and toes on fire. A lifetime of hunting helps him push past the fog and he sits bolt upright, barely aware, but still ready to fight.
"What the fuck?"
His hands are wrapped up inside thick wool mittens. When he kicks the blankets off, his feet are in what looks like three pairs of socks.
"I don't think anything's gonna drop off," Sam says.
Dean's hand instinctively reaches for his dick. Just to check. "Where the fuck are we?"
"Lebanon Motel," Sam says. "Bunker's still a little frosty."
It's probably the only motel in the country they haven't seen the inside of. "How'd you get in?"
"Salt and burn did the trick," Sam says. "Door cracked right open. I dragged you out of there. Made sure you got warm."
Dean nods. "Thanks. Guess we gotta figure out what did it, now."
"It can wait," Sam says. "For now, get some rest. You need it."
Dean doesn't have the energy to argue.