Rabbit hole

A rabbit hole is the entrance to a rabbit's burrow or warren.

In Lewis Carroll's "Alice's Adventures in Wonderland", Alice follows a mysterious white rabbit into a rabbit hole to enter 'Wonderland', an absurd and improbable world inhabited by many strange characters. This usage has helped make the phrase refer more generally to any portal into a different or strange world, such as:

*The character Morpheus in the movie "The Matrix" uses this metaphor when he offers the character Neo the opportunity to enter "the real world".

*In the film "What the bleep do we know!?"

*The term is used in alternate reality games to describe the initial page or clue that brings the player into the fictional world of the game.

*"Rabbit Hole" is the name of a play by David Lindsay-Abaire.

* Rabbit Hole Ensemble is a theatre company in New York City.

By extension the term has also come to signify any event which triggers a completely unexpected situation.