Rabbit hole

The wikipedia says:

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... ... The term has also come to signify any event which triggers a completely unexpected, bizarre situation or paradigm. --http://en.wikipedia.org/wiki/Rabbit_hole

In the wonderful world of Alternate Reality Games, the Rabbit Hole is a device which introduces the game to players. Of course, a good rabbit hole doesn't simply walk up and say "Hello, play me!" A good rabbit hole will slink quietly into the back of the room and pass notes to everyone in the class but you, compelling you to wonder what all the fuss is about.

For perplex city, the rabbit hole was a series of newspaper article fragments, strategically placed around the world (See: Newspaper Text)