There currently is one option to travel by night train from Munich to Kiel, taking between approximately 11 and 12 hours: Namely the ICE 618 operated by DB.
Deutsche Bahn (DB) exited the actual night train business in 2016. However, it operates around a dozen Intercity and Eurocity trains that run exclusively at night. In these night trains, there are only first and second class seats. The lights stay on all the time and there is no way to recline the seats.
For the next 7 dates with connections, the cheapest offer starts at 18 EUR. Check our connection pages below for all availabilities!