Rail itinerary ideas needed

How long is this trip?

Oops...sorry. Original post updated to add we will be there for 10 days,

For 10 days my suggestion would be to fly to Zürich and focus on Austria, Switzerland and northern Italy. Not too long distances, plenty of night trains and great scenery. No countries famous for their beer though.

Your question is so broad that it is really difficult to make any recommendations. With ten nights the most you are going to do is three cities. It could be any three cities. Munich, Vienna, Budapest. Certainly use an open jaw ticket to save time and money. Pull the guidebooks, the travel DVDs from your local library and decide what appeals to you. We respond better when the question is a little more precise.

Yep, I know its broad and that part of the reason I am here. Was looking to hear about others' past rail itineraries to see what worked for them. We do tons of research before we travel, so I am not looking for someone to do the work for me, but just thought hearing about itineraries that worked for other people would be helpful.

Def will be flying open-jaw; we do that most every time we are there.

If someone said to me “You have 10 days anywhere in Europe by train” I would pick one country. Of your list, Switzerland is a stand out to me, on of my favorite fall destinations as we go every year. Lovely weather and the best transportation system anywhere.

Scotland is tough solely by train, IMO.

How about Munich to Salzburg to Vienna. Melk and Bratislava that could be seen as day trips.
Another good trip would be Budapest, Vienna and Prague.
Or, Munich, Innsbruck and Venice.

I'm cold/wet-weather averse and would not go to Scandinavia in September or October. YMMV.

In any one of the countries you mention, trains can easily get you to more than enough destinations to fill your time. Buses often fill in where trains leave off, such as along the north or south coasts of Spain, but with only 10 days to travel, you're not likely to get so far that you need a bus.

Of course, hopping between different countries generally takes longer and would be a prime reason to compare flying. Some people start to look at flights once a train ride exceeds 6 hours. Or again, this could be a reason to narrow your focus to destinations that are closer together. (On the other hand, David has named some options in central Europe where the major cities in each country are closer together.)

Rick’s Train Travel Time & cost Map gives you an overview of faster train travel times in hours, primarily for international and longer-distance routes.

To get down to more detail between any two cities on the national railways of Europe, Looking Up Train Schedules and Routes Online gives you the Deutsche Bahn train schedule link and tips for using it.

How about Berlin-Leipzig-Dresden-Prague? You could satisfy your car yen in Germany, with side trips to places like Erfurt, Gotha, Eisenach, Quedlinburg, Dessau-Worlitz. I agree that three big cities are enough for 10 days. If I were going to Europe in Sept-Oct, I would try to capitalize on the end of the August vacation season, maybe with Tuscany or the Amalfi Coast or some place that is impossibly crowded in high season. Well, that includes Cesky Krumlov!

Consider London and Great Britain. The countryside is amazing. Don't miss places like York, Durham, Winchester, Stratford Upon
Avon, Oxford, Cambridge, Salisbury, Canterbury, the Cotswolds, Cardiff, St. David's Wales, Tenby Wales, the Lake District, and that is just England and Wales.

It is difficult to respond to your post because you are talking in "countries" and not in locations. Having been to "Italy" before does not help us narrow down what you might want to visit on a return trip to Italy - same with the other countries you mention.

At some point, we would like to visit Norway, Denmark, Prague, Switzerland, Spain, and Scotland...

Prague only? Does this mean you have zero interest in the rest of the Czech Republic?

...possibly flying into either Zurich or Prague... Def will be flying
open-jaw... We like history, great food, scenery, and have an interest
in beer.

Based on these comments you might figure out your own start/end points and include some of the following places, which I feel meet most of your criteria...(you may need to consider using Vienna, Frankfurt or Munich airports, depending on what you come up with.)

(CH) Zurich - Zug - Luzern - Schaffhausen - Stein am Rhein
(DE) Tübingen - Bamberg
(CZ) Plzen - Prague - Ceske Budejovice - Ceske Krumlov
(AT) ??? several good options. https://www.austria.info/us/austria-a-singular-journey-a-lifetime-of/austrian-railways

In August 2018 we did Prague - Olomouc - Budapest - Vienna by train. The longest leg was maybe 4 hours and there’s always something to see out the window. The Budapest to Vienna train was very crowded and we were very glad that we had paid extra to book a seat not just a ticket as some people had to sit on the floor because they hadn’t booked seats. I always book directly through the national railway websites not through a third party site. Booking 3-4 months ahead can mean great discounts.

I use the rome2rio website for travel planning as it shows all options to get from A to B including local buses which might be cheaper and quicker than the train.