This past Sunday we covered the advanced level grammar form ~다니.
Why is this form advanced? Well using it and understanding it isn't hard at all (beginners could probably understand it just fine). The "advanced" comes from it actually being two forms (or three) that work as one form. And in order to use this form, you'll also need to already have a mastery of the quoting forms - and that's something that first requires a lot of practice.
But with the quoting forms ready and a few example sentences, you'll also be well on your way toward mastering this form too.