Hello,
I'm looking into doing an 18-20 day solo trip in Germany, Austria, and the surrounding area. I was wondering if anyone had recommendations for historical sites (especially castles) and historical museums worth checking out?

There is a great deal to see in the categories you mention. Start by getting a copy of the Fodor guide to Germany and the one for Austria and doing some research. Then we can answer more specific questions.

In Austria, you will certainly want to visit Vienna (fine museums, old churches, several palaces, the Spanish Riding School) and Salzburg (castle on the hill and charming old town).

In Germany, we really liked Munich. It has the lovely Nymphemberg Palace, the Residenz (home of the ruling families for centuries and a very good museum now), and much more. The municipal art museum is a gem.

Two of the famous castles in Germany are Neuschwanstein (it was more or less the basis for Sleeping Beauty's Castle) and Linderhof. Read about both and you'll put them at the top of your list for castles in Germany, although there quite a few others worth a visit or even a detour.

You might consider visiting Oberammergau, home of the Passion Play. It's a very pretty small town, with houses painted in all sorts of lovely designs. Good shopping, too.

For Germany you need to look in cities that managed to avoid most of the bombing damage to see real history rather than pastiche. In the country side things are easier especially where old castles still abound.

Depending on what you mean by history Neuschwanstein is a modern building. I'd look at Trier which has Roman buildings still stading and certainly some from 1000 and 1400. I'd also try to visit Ulm old town centre which has painted buildings from the 1400 (though repainted of course).

Also look out for Grand Ducal properties (Germany was carved into GrandDuke bits by Otto 1 (I think) and some of these amazing buildings are still extant and open.

I'd also look out for churches along the Austian/Swiss border for when the inhabitants were some of the poorest in Europe and could not read leading to painted ceilings depicting the bible, now many exist only in tiny villages.

"Depending on what you mean by history Neuschwanstein is a modern building."

Yes. It's actually an unfinished building where work stopped around 1895, I think, which is well AFTER the age of castles, as any history buff knows. Unlike real castles, this one was built as a residential palace - by a Bavarian King named Ludwig II, an eccentric who added a fake castle exterior to his lavish and expensive home. While Ludwig was an interesting character, the building itself played little role in history. Ludwig lived there just 6 months before his death, and afterward it was unused except as a tourist attraction.

"Two of the famous castles in Germany are Neuschwanstein (it was more or less the basis for Sleeping Beauty's Castle) and Linderhof."

Linderhof was built by Ludwig as well in the same period; again, it's a palace, like Versailles is a palace, not a serious castle. So... although they attract tons and tons of tourists who might think of them as castles, it's more correct to say that these are two famous BUILDINGS in Germany they simply cannot be placed at the top or the bottom of any list of "castles."

Medieval castles OTOH played a huge role in European life; while they are scattered around Germany to some extent, many are in a sorry state now. But the Upper Middle Rhine Valley (near Frankfurt) has a large concentration of them on the cliffsides and river banks. Some are in ruins, some have been rebuilt, and a handful of them, like Marksburg in Braubach, were never destroyed and were kept up well enough that touring them now is like time travel. Most lie between Koblenz and Bingen:

http://www.loreley-info.com/eng/rhein-rhine/castles.php
http://whc.unesco.org/en/list/1066
http://www.marksburg.de/en/

Nearby in Remagen is a good WW II museum:
http://www.bruecke-remagen.de/index_en.htm

In the Nahe River Valley (one of the Rhine tributaries) is an open-air museum where you can get an angle on local life over the past 5 centuries. Really interesting.

https://www.freilichtmuseum-rlp.de/b...h-information/

Mainz, a city to the south of the MRV, has some interesting museums on a variety of historical themes, like the development of the printed word, shipbuilding, ancient Rome ... as well as churches and other places of interest.

https://www.tripadvisor.com/Attracti...alatinate.html

All the places I've mentioned are easy to see by train if that's how you're getting around.

So altogether, maybe with Trier as bilboburgler has suggested, this area might be a good target for a few days.

Hey,
so you should definitely check out Berlin, obviously! It has so many museums, you can spend weeks there.
Hamburg is full of old buildings too, just a three hour bus ride (really cheap) from Berlin. And southern Germany will be of interest for you too.
Great old buildings and history. Otherwise check out spain, italy, france, romania has some great history or budapest.
Enjoy

Trying to imagine how Hamburg, famously bombed flat, has anything old, the odd bit from WW2, perhaps like the submarine museum down on the coast and the odd bit of revamped Jugnestehl

still the Tourist office is pushing this stuff http://www.hamburg-travel.com/attrac...toric-hamburg/

My BIL had a piece of 1750s furniture restored by a German firm once, never gain, they changed everything and claimed it was restored, no they just used the orginal as a template, beware pastiche.

<<Two of the famous castles in Germany are Neuschwanstein (it was more or less the basis for Sleeping Beauty's Castle) and Linderhof.>>

Completely lost as to how Neuschwanstein could be the basis of Sleeping Beauty's castle when Perrault wrote the story in the 1600s and Neuschwanstein wasn't built for another 200 years. Perrault based his sleeping beauty castle on Chateau D'Usse.

If you're referencing the Sleeping Beauty castle at Disneyland, that's no reason to see Neuschwanstein.

My all-time favorite German castle is Burg Eltz. To visit it, you could stay at the nearby Hotel Haus Lippman in Beilstein on the Mosel River.

Yep, Sleeping Beauty's Castle is on the Loire near a Nuclear Power Station.

Burg Eltz is a good visit, well worth the walk

Re Eltz: Drive to Landhotel Ringelsteiner Mühle, park there and walk through the woods along the Elzbach River to Burg Eltz. The castle itself is still a residence and an unmolested example of German castles (never sacked by the French). They have an EN tour and a small museum. There are two food services and I like to have lunch on their patio before walking back to the car. If you don't dine at the castle, the Ringelsteiner has a dining room and also a fresh supply of pies and cakes to complete your hike.

I notice you also tagged Belgium and Czech Republic. I don't think you have time to do 4 countries well in 18 days, but you could potentially be driving through Czech Republic, depending on your itinerary.

The most famous castles there include the Karlštejn Castle in Bohemia, and the Prague Castle in Prague. Some websites state that the Prague Castle is the largest in the world. The Strahov Monastery next door with its amazing ceilings is worth visiting.

Don't miss the Jewish historic quarter, which includes the oldest active synagogue in Europe.