Re: Travelling Europe
Do it with a tent, or hostels.
If doing a month, and you have a decent car, it’s not beyond the imagination to drive.
It dep new what you want, culture, beer, nature, history (including WWII) etc. Especially with some of the countries you mention, the cities can be a distance apart.
You could minimise travel by grouping stuff together too
Liege/Cologne/Aachen for instance, then down to Munich/Stuttgart/lakes/Alps, then to Nice/Monaco/Italy (actually, forget Monaco)