rabbit hole

noun
  1. 1

    (usually with article) A bizarre world, where everyday rules do not apply, or a way into such a world.

    โ€œThese mushrooms will take you down the rabbit hole, man.โ€

  2. 2

    (by extension) A time-consuming tangent or detour, often from which it is difficult to extricate oneself.

  3. 3

    The initial clue that leads to an alternate reality game.

Source: https://en.wiktionary.org/wiki/rabbit%20hole