To look at the differences between European countries is the best way to organize it to group them according to their geographical position or cultural background. In this way we can find southern Europe, Scandinavia, Great Britain and Ireland, Eastern Europe, Benelux and France and Central Europe. To determine if a country is included here and there can be difficult sometimes and to define the area I should speak, I would like to call them as German-speaking countries, which will be Germany, Austria and Switzerland.
From my point of view, the execution of this area is one of the things you must do if you plan to travel to Europe, and I strongly recommend organizing a route by train that takes one of the discounted tickets in this area, such as sightseeing from Comfort in Your window can be an experience of itself, especially if you try some of the scenic roads that Switzerland offers. They are not cheap I have to say, but you will never forget it.
As a travel proposal, I would first of all like to say something to the non-European traveler. Reaching Europe from your home country can offer many opportunities, especially if you can land in many countries. Lufthansa, Swiss Air and Austrian Airlines cover almost all possibilities. In any case, from my personal experience, flight to Frankfurt will almost always give you a price advantage because of the low taxes and at the same time it works as the headquarters of most low cost airlines that can bring you to any part of Europe for much reduced prices.
If you come from any part of Europe, I also recommend flying to Frankfurt and then taking the train from there. We start in Germany, but the road will soon leave the country. The idea is to go south through Baden-Baden. It could be a first stop, with a relaxing visit to the thermal pools. Further south you will come to Freiburg, a city located next to the heart of the Black Forest, a deep forest where you can find many activities, from hiking trails to adventure, including some extraordinary nature areas like waterfalls.
If you continue south you will enter the Swiss territory. Bern is the first city to come to you, but if you have time you can also get to know Geneva in the west. The capital is beautiful but is probably not the most famous city in the chocolate country. If you take a train ride south again you want to reach the city of Interlaken. As the name suggests, it is located between two large lakes. It's not a big city, but nature is getting lost there. From there I would take a trip to Grindelwald and enjoy 100% clean air of more than 2000 meters, surrounded by green hills and lakes. If we had to find a place for the paradise in Switzerland, probably this little city would probably take the first prize.
When you return to Interlaken, you can now point to Lucerne, make a quick visit to the Old Town and continue east until you reach Zurich, contrasting with its modern architecture, compared to the aforementioned cities.
After your visit to Zurich, I would take a train to the Austrian countries. The main attraction in Austria will be the landscape of high mountain ranges and green fields along with the magic of the old towns. My suggestion is to take a night train from Zurich to Vienna, spend at least 2 days in the capital, and then return to Salzburg and Innsbruck. If you have time, take a round trip to Linz.
Time for Germany has come back, and then the road takes you to Munich. It's not just the beer that has made this city famous, but of course you're more than welcome to take a little! From Munich, and before going north, I suggest I will make a trip to Füssen. It is a very small town but they have some of the most enchanted looking castles you can ever imagine. After this short visit, take a nightly train from Munich to Berlin and spend at least 2-3 days in the capital. Berlin has a really dramatic history in the development of Europe and there are buildings to remind it. Try to make the visit to Berlin as cultural as possible and you get the most of it. If you have some extra time, I encourage a 1-day visit to the nearby city of Potsdam. The gardens are absolutely amazing.
Finally, I would say that it really depends on your time left or the journeys left on your rail ticket, but visit to Hamburg and especially to the cathedral of Cologne can be a very good end to history. Go back to Frankfurt by train again and take your flight to your home country.
If you want to discover some extra things, you can always take the train that goes to Denmark with a big ferry to cross the sea, or hello to the small but intense Benelux region or Eastern France. Everything depends on you, but here you have the basics of a very complete route in this paradise of history and nature, together on a journey that can take 15-20 days.