Hi, broad question I know. But I've recently become an enthusiast of history in the last 6 months and have 42 days in Europe over April and May this year. I'm planning on using it to visit as many muesems and historical sites as possible. I land in Frankfurt, Germany and plan on travelling to the following cities; Cologne, Hannover, Berlin, Paris, Barcelona(possibly), Krakow and Prague.
Also on my list of possible countries to visit are Belgium, England, Switzerland, Austria and Italy. Anywhere you found interesting I'd like to know about, so I can research prior to landing in Europe.
I'm mostly interested in WW1 and WW2, although recently have taken a huge liking to Alexander the great and the early Roman empire. Any suggestions are very welcome and much appreciated.
Hi there. A similar question was asked on /r/travel. You can find that post here: https://www.reddit.com/r/travel/comments/4ak2fj/what_is_your_favorite_museum_rtravel/
In England, go to the Imperial War Museum (which I think has the Churchill War Rooms). There is also the army museum near London.
If you want to go to Switzerland for a day or two you'll find both roman ruins and defenses from WW2 quite close to each other along the Rhine. These are what I'm talking about:
Military Museum Full-Reuenthal (choose english as language in the top right corner for info)
Both are located in the Canton of Aargau and thus close to a lot of castles if those interest you. The most important ones are probably Lenzburg Castle and the ruins (and some intacts parts) of Habsburg Castle (The origin of the House of Habsburg]. Major downside: Aargau has no Alps, only some hills and small mountains from the Jura Mountain Range so you wouldn't see any amazing alpine landscapes there. Another downside: Switzerland is quite an expensive country.
Other stuff in Switzerland that comes to my mind:
All the major Cities (Basel, Bern, Zürich, Luzern) are worth a visit. Bern has a great Historical Museum and Zürich has the Swiss National Museum.
Roman Site & Museum in Avenches
For a general Information about historical stuff in Switzerland I'd recommend to look at this page.