Probably the cheapest public transport ticket in the world!

 

From June 1st all citizens and visitors can travel freely in Germany on all forms of public transport, local and regional (excluding InterCity trains), for only €9 per month. This offer is currently valid for the months of June, July and August 2022. Here's hoping they might even extend it. Buying the ticket is a sinch - they are available in the machines on every station platform. Bag one on your arrival in Germany and travel almost for free!
For more detail read all about it on ExBerliner