Down the rabbit hole, to me, refers to rabbit burrows having many offshoots and branches - a network of tunnels. So you pop down the rabbit hole and begin exploring. Maybe you have some idea of what you think you'll find or where you'll go, but once you've traveled a maze of tunnels and find another place to pop up, you may not be anywhere near where you started or where you thought you'd end up.

To really go down the proverbial rabbit hole, it's like striking out on an adventure, taking the twists and turns as they come, discovering what is there before you and not really knowing precisely where it will take you. It's getting off the straight and narrow track of programed reality and digging in to see what really lies beneath the surface, imo, as it's used in many places today.