Schwarzfahren

"Schwarzfahren" is the act of using the public transport system for free (for details see tip: subway cops). If you want to engage in this sport, you need to either be a fast runner and an excellent liar. Once you get caught, you will get fined. If you get caught too often, you may be denied access to public transport altogether. Talking your way out of it ("I have a daily/weekly/monthly ticket and left it at home/the hotel") will not help much. Your ID can get confiscated. To retrieve it, you will need to bring the ticket to public transport headquarters, and you will still have to pay a (slightly lower) fine. Ok, being a tourist might help you somewhat. Generally speaking, though, Schwarzfahren is not advisable.