rabbit hole
noun
Definitions
(usually with article) A bizarre world, where everyday rules do not apply, or a way into such a world.
Example: These mushrooms will take you down the rabbit hole, man.
Synonyms:looking glass(by extension) A time-consuming tangent or detour, often from which it is difficult to extricate oneself.
The initial clue that leads to an alternate reality game.
Synonyms:trailhead