1. an endless journey of learning/research/information
fall down the rabbit hole
This idiom is a pop culture reference from the novel 'Alice in Wonderland' and refers to a process or journey that becomes more unpredictable, unexpected and strange as you continue. You might use this to explain that you are going on an unknown journey or that you expect problems or strange things to happen. "I have never had a client in Japan before, this will be a journey down the rabbit hole for me."