Behold... The Dean-cave. Or Fortress of Dean-a-tude. Just -- still trying to figure that one out.
The Dean Cave (or Fortress of Dean-a-tude) is an area of the Men of Letters Bunker which Dean has turned into a recreational room for himself and Sam. The room's layout includes a Foosball table, a jukebox that only plays vinyl, a bookshelf of vinyl records and cassette tapes, double La-Z-Boy recliners, and a bar (still a work in progress) which consists of two cinder blocks and a bit of wood on top of an alcohol-filled credenza. The walls are decorated with AC/DC and Led Zeppelin posters, as well as a framed vinyl record of Kansas' Point of Know Return album, an Impala poster, and neon beer signs and beer posters, with four kegs hanging from the ceiling.
After Sam and Dean fight a giant possessed green dinosaur plushie in a pawn shop, the owner offers them anything in an act of gratitude. Sam attempts to turn him down, but Dean takes him up on the offer and chooses a large flat screen TV.
Back at the Men of Letters Bunker, Sam is researching cursed objects to try and figure out what they just fought. Dean excitedly enters the library and asks Sam to come with him. After some prodding from Dean, Sam agrees and is taken to the Dean Cave -- a recreational room Dean has set up in the Bunker. Dean points the remote at the TV, which begins to light up purple before Sam and Dean are hit with a beam of purple light that pulls them into the TV. Quickly realizing they are cartoons, they try to figure out what happened. When Dean sees the Impala has been animated as well, he suggests to Sam they work the case and drive until they find something. They soon discover they were pulled into the world of Scooby-Doo. When Castiel later returns to the Bunker, he is also pulled into the TV.
They eventually find out that the soul of a dead boy is tied to a pen-knife that Jay placed inside the TV. When they return to the real world they destroy the TV, find the knife, and burn it, releasing the boy's spirit. They later arrest Jay for tax evasion.