rabbit hole

Meanings

1. A bizarre world, where everyday rules do not apply.
2. A way into such a world.
3. A time-consuming tangent or detour, often one from which it is difficult to extricate oneself.
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.

Etymology

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