The Men of Letters Bunker has had quite enough of Dean pining for Castiel, and it decides to intervene. To be fair, the Bunker interferes a lot, and usually for good reason. For example when it vanished the big garage doors, it prevented Dean from taking Baby out with clogged catalytic converters, saving her from spontaneously setting on fire halfway down the road. And when he and Sam ran out of room to manspread into, an entire extra floor appeared as if by magic.
This time, it's locked Dean and Castiel inside Cas' room, which is great as long as they have plenty of episodes of Stranger Things left to watch, and the Bunker has some conditions if it's going to let them back out--Dean has to confess his feelings.
Which he does.
And then one thing leads to another...
Stranger Things and Eldritch Bunkers is a humorous take on the Trapped in an Elevator trope, with a little bit of One Room, One Bed mixed in.