aelle_irene asked : : What are the historical sites you recommend visiting for those who want to avoid 20th Century History?
Given Berlin was heavily bombed in WWII and had to be rebuild, it's next to impossible to avoid the 20th century, but there are still sites from previous centuries to visit and enjoy, of course. Bear in mind I myself am talking as a tourist here; I never spend more than a week in Berlin, and the week was decades ago; in more recent years I was only there for one or two days.
In general, since you're travelling in May, I reccommend a boat tour on the Spree, like
this one. It will surprise you with how much greenery Berlin has to offer and give you a true sense of location of the city core. On to buildings and museums.
Now: in Berlin itself, there is the
Museumsinsel, the island mid-River Spree full of interesting museums. (Link goes to the English version of its website.) This is where you find the famous bust of Nefertiti and a lot of other pieces of Egypt's Armana period, for example, the Pergamon Altar (currently getting renovated, but there's a 3 D model), the Ishtar Gate, but also a lot of 19th century art (including arch romantic Caspar David Friedrich). I can also reccommend the big museum shop for all the museums located near the James-Simon-Gallery, if you want, say, a mousepad that looks like a Persian silk carpet, or that shows all the Roman emperors, or books about any of the eras and people featured in the museum (not just in German, also in English).
Then there's
Charlottenburg Palace. I just linked you to the English version of the museum website again, but for a recent personal pic spam (from last year) of this baroque palace and its park, check
this out. Aside from offering really well restored Baroque and Frederician Rokoko, this palace also includes in one exhibition a panoramic view of mid 19th century Berlin, a city that was gone even before WWII. Also, if you don't have the time or inclination of joining a tour, all the rooms offer biligingual or trilingual signs (i.e. German, English and French) explaining the context of what you're seeing, and you learn a lot about Prussian history.
We'll return to (some) Hohenzollern later, but on to non-royals. The
Mendelssohn Remise, at the location of the Mendelssohn bank, is a small museum devoted to one of the most fascinating artistic families in German cultural history. The most famous members were Moses Mendelssohn (the 18th century philosopher), Felix Mendelssohn-Bartholdy (grandson), the composer, his sister Fanny (equally a composer and musician), and their aunt Dorothea (nee Brendel) Schlegel (writer and translator). Depending on how into the Mendelssohns you are, you can also visit several of them (including Felix and Fanny) at the "Friedhof vor dem Halleschen Tor", where there is also a crypt reworked into a permanent museum on the history of the Mendelssohn family. Other famous artists buried at the same cemetery include Rahel Varnhagen (famous Jewish femme des lettres of the late 18th and early 19th century) and E.T.A. Hoffmann. The Mendelssohn Society even organizes
In the Footsteps of Fanny tours through Berlin, as well as
In the footsteps of Rahel Varnhagen through Berlin.
Speaking of Berlin history for special interests, there's the
Hugenottenmuseum. When Louis XIV revoked the toleration edict of Nantes in the later 17th century and tried his best to kick all Protestants out of France if he didn't terrorize them into converting, a really huge part of them ended up in Brandenburg and Prussia in general, courtesy of its ruler, another Frederick William, "The Great Elector" (Prussia wasn't a kingdom yet). This is why for a long time you had a lot of French speakers there, why for example one of Germany's most famous writers, Theodor Fontane, grew up pronouncing his last name the French way (his father being Louis Fontane, and grandfather Pierre, and so forth), and why there is a museum devoted to the Huguenots in Berlin. The "French Colony" really was an important part of the city for several centuries.
If you have enough of buildings and the weather is nice, I reccommend a visit to the
Viktoriapark in Kreuzberg. This park was created in the 19th century and named after Queen Victoria's oldest daughter Vicky, she who married the Prussian Crown Prince who only briefly became Frederick III, the mother of (boo, hiss) Wilhelm II. As the website I just linked you to says, it is however nothing like an English park but goes for wild landscape romanticism with waterfalls. There also some nice beergardens where you can sit down and have a drink and something to eat.
Outside of Berlin:
I really reccommend a trip to Potsdam, which is easily reachable from Berlin Central Station by train, bus or tube. Mainly, of course, because that's where you'll find
Sanssouci Palace and Park, i.e. Frederick the Great's palace(s) (there are actually three belonging to the overall Sanssouci complex). I just liinked the main palace's website in English again, but of course, yours truly has personal pic spams to offer:
Sanssouci in summer (that's the pic spam with the interior as well),
Sanssouci in spring time (only outside pics). It's 18th century "Frederician" Rokoko at its best, and surrounded by a beautiful park. If you like bread: the famous mill next to the main palace actually offers freshly baked bread for sale.
Bonus reccommendation:
Now, this inevitably and poignantly does include the 20th century. But it shows all the centuries before as well. I can really reccomend the Jüdisches Museum, the Jewish Museum of Berlin, which you can find
here. The core exhibition, about Jewish life in Germany, goes back all the way to the time of the Roman Emperor Domitian. One highlight is the story of the very successful Renaissance Jewish merchant woman Gickl of Hameln, whose memoirs, the first written by a woman in Jiddish, I believe, were later translated into standard German by none other than Bertha Pappenheim (a Jewish feminist who also as Anna O. entered the history of psychotherapy as she was one of Freud's earliest patients). Obviously, a considerable part of the museum does tell the story of the Holocaust, because how could it not? But if you can avoid it, you can stop before that point. The story of Jewish Germans is just so fascinating and important - for Germany in general but also for Berlin in particular - that I think it's worth visiting.
The other days