If you live in the Pfalz area of Germany....you have opportunity to buy a 24-hour railway ticket via your local machine or railway station.
The deal is this....24-Euro....for a ticket that starts in the morning hours and ends at midnight....giving you unlimited travel in the Pfalz state and Saarland as well. The catch? You can't travel over the stateline of the two regions.
The plus of the 24-Euro ticket? It's for you AND up to FOUR friends.
So you could board the train in Kaiserslautern, and head up to Mainz in the early morning hours and spend all day walking around the city with your friends on a Saturday, and come Saturday evening....take the last train out of Mainz to return to Kaiserslautern. No hassle on driving, parking, or getting lost.
Each German state has it's own German ticket, and each is priced different (Hessen is 32-Euro, Bavaria is 23-Euro).
For a group of five, it's a fantastic deal.