Occasionally in Germany....someone will accidentally tell you some tidbit about traveling that isn't widely advertised.
When I was here in 1984....someone made some minor comment in some base publication about a three-day German railway pass for roughly 110 Deutsche-Marks. (roughly $40 at the time). I was curious and asked two simple questions at the travel office on base. I thought it was a great deal. So I planned a simple three-day trip on an American holiday weekend to see a chunk of Germany in 72 hours. Then the on-base travel office said fine, but we don't sell the ticket. You have to buy it direct from the Bahn clerk in town.
I went down on a Friday night at 10 PM and bought the 72-hour pass. And I rode across various parts of what was then 'West Germany' along the northern third of the country. It was cheap, efficient, and perfectly safe.
Today? The ticket still exists but you have to ask more questions because it's a bit different.
For example....you can buy a flex-ticket for three days of travel within one month....2nd-class seat....for 191 Euro. If you want first-class seats....it's 258 Euro. You start on day one....travel to Berlin and spend four days there....then do travel day two and spend three days in Erfurt......then do travel day three and spend four days in Munich....then use travel day four and return back to the starting point.
If you want seven days of flex-travel in one month? It's 272 Euro.
Five consecutive days of travel at 2nd-class (no flex or one-month period)? That's 213 Euro. Roughly $250 American. Upgrade it to 1st-class seats? 288 Euro. Ten consecutive days at 2nd-class? 309 Euro.
If you wanted to do the 'adventure' side of this.....think of one single region where you'd like to hit three medium-sized cities over a ten-day period with the flex-ticket. You need four total days of travel....so the ticket for your requirement is 205 Euro (upgrade it to first-class for 277 Euro).
Interested? Just Goggle up flex-ticket and Bahn, and the page will come up with the options and cost.
The thing is....you really need to plan this out and have a decent agenda. It means traveling somewhat light, and gleaning over a schedule to know how many hours it takes to get from X to Y, and what options exist. I also would avoid German holiday periods like Easter because traffic is heavy and seating limited.
For my weekend trip in 1984.....I actually started out at 12:05 out of Kaiserslautern....leaving for Frankfurt (the last train of the night). I had to sit around for three hours in Frankfurt at the time of arrival.....waiting for my long-distance train going to Hamburg. Most people aren't that thrilled for this type of travel.
So, just some travel advice.