Intrepid Fictioneer

When characters breach internal fourth walls to go on adventures in books, films and so on. Generally they travel into one or more books or films to become part of the plot, or, at least, to observe the plot first hand. This often forms part of an allegory or metaphor for escapism, the idea that the imagination allows a reader to 'enter' a work and subconsciously cast themselves as an observer or a main character. This is one reason why the lead characters of books are often very vaguely or loosely described, allowing the reader to assume their identity as a form of role-play.

Compare and contrast Trapped in TV Land. See also Reading Is Cool Aesop. Not to be confused with From Beyond the Fourth Wall, when the fourth wall is the one between us and them.

Anime and Manga

 * In Monster Rancher Genki travels to the monster world through a computer game, however this example may be a subversion since . In particular the  and the fact that  speaks volumes. Not to mention that.

Comics

 * Fantastic Four: True Story by Paul Cornell. The FF travel through various well-known works of literature.
 * Justice League of America villain the Queen of Fables. She is eventually defeated and trapped when the heroes trick her into entering a copy of the US Tax Code: a work that contains no imagination and so one from which she cannot escape.
 * In Grant Morrison's The Filth, The Hand uses Intrepid Fictioneer tactics to mine cheesy golden-age comics like Secret Original for Weird Science gadgetry.

Film

 * Last Action Hero, starring Arnold Schwarzenegger. A young boy gets sucked into the latest instalment of a fictional action movie franchise using a magic ticket and try to stop the villain of the movie from using the ticket to wreak havoc in the real world.
 * The Neverending Story and its two sequels where a boy travels to the world of Fantasia by reading the book of The NeverEnding Story and having to save the world inside the book from the various evils that wish to destroy it.
 * In The Pagemaster Richard travels through a mash-up storybook world based around tightly and neatly divided Adventure, Fantasy, and Horror, genres and is, essentially, travelling from one book to another trying to find his way out.

Literature

 * Jasper Fforde's Thursday Next books are the trope namer and codifier here. Thursday finds out that fiction has a 'behind the scenes' and that all books are intrinsically linked, with characters actors in the work. Thursday goes on to travel from book world to book world. Incidentally, Fictioneer is a derogatory term meaning a writer of large amounts of tatty pulp fiction.
 * Only You Can Save Mankind, Johnny and other characters travel into the titular computer game and rebuild large parts of it with their imaginations. Their actions alter the game in real time and actually.
 * The Neverending Story, where a boy travels to the world of Fantasia by reading the book of The NeverEnding Story and having to save the world inside the book from the various evils that wish to destroy it.
 * Harold Shea.
 * The Inkworld Trilogy has select few characters who are able to send people and objects into and out of stories when they read out loud.

Live Action TV

 * Lost in Austen.
 * The Tenth Kingdom subverts this in that it is revealed that most fairytales were written by people who wandered into an actual fairy world.

Theatre

 * In Bunbury: A Serious Play for Trivial People, Bunbury and Rosaline become The Gump as they journey through the Western canon, meeting other unseen characters. Bunbury even becomes Godot.

Video Games

 * In Myst, this was the premise. Certain people had the power to create worlds by writing about them in books (or something like that). They could travel into them -- and, if the book, which then served as a gateway between worlds, was damaged, they could be trapped.

Web Original

 * SCP Foundation's SCP-423, also known as "Fred", a roving character who can hop between books for fun. SCP-826 is an pair of bookends that allows one to enter any work of fiction placed between them.

Western Animation

 * In the Futurama episode "The Day the Earth Stood Stupid," Fry travels into books and assumes the roles of various characters.
 * Gumby's theme song points out that "he can walk into any book," and he does so frequently.
 * In The Fairly Odd Parents: Channel Chasers, this happens to Timmy, also the episode "Shelf Life" has Timmy chasing Tom Sawyer through different books after he stole Cosmo's wand.
 * The Teen Titans animated has them chasing Control Freak through a bunch of different TV shows.
 * In Blues Clues, the main character, Steve, would "scadoo" into books to find clues. The story itself seems to take place inside a book.