rabbit hole

noun

Etymology: From rabbit + hole. Extended senses reference Alice's Adventures in Wonderland, where Alice travels down a rabbit hole into a bizarre world.

1. A bizarre world, where everyday rules do not apply.
2. A way into such a world.

   “These mushrooms will take you down the rabbit hole, man.”

   “You take the blue pill, the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill, you stay in Wonderland, and I show you how deep the rabbit hole goes.”

3. A time-consuming tangent or detour, often one from which it is difficult to extricate oneself.

   “Near-synonym: rabbit trail (regiolectic)”

   “I'm also a fan of a really obscure book series, but that's a rabbit hole that we won't get into.”

4. The initial clue that leads to an alternate reality game.
5. Used other than figuratively or idiomatically: see rabbit, hole. The entrance to a rabbit warren or burrow; the whole warren or burrow.

   “The rabbit-hole went straight on like a tunnel for some way, and then dipped suddenly down, so suddenly that Alice had not a moment to think about stopping herself before she found herself falling down what seemed to be a very deep well.”

   “As the limber gunners went to the rear, his horse trod in a rabbit-hole and came down, throwing him into a depression of the ground.”