Talking to a computer in a tiny room for 5 or 6 hours, and some controlled conversation. It's hard, kind of weird, but good. Very helpful if you apply yourself, but a lot of people decide they don't like it after 3 days and kind of tune out. If you go, please don't be one of them. I wasn't one. I achieved fluency and kept it for a year. I practiced less and eventually lost it. I really recommend it.