On recommendation from a trusted source, we went on a 'Fat Tire Bike Tour' of the main historical sights of central Berlin - possibly one of our best decisions yet!
With English speaking fellow cyclists and a very English guide, we learned a lot of quirky facts about Berlin and met some lovely people over beers at the lunch stop. Cycling in the city was also a steep learning curve - no helmets, and right in the mix of traffic and on the wrong side of the road! But that was the only challenge - as Berlin was originally a swamp there is not even one slight incline, making the 4-5 hour tour a breeze.
The major sites we visited included Alexanderplatz; Babelplatz (site of the burning of the books); Humboldt University (Nobel Prize recipient factory); Rathaus (city hall); Konzerthaus (fascinating story of the French and German churches here); an existing preserved segment of the Berlin Wall; a guard tower; the Jewish Memorial; the site of Hitler's bunker (aka the most famous carpark); the Tiergarten (ate lunch in the Biergarten within); the Reichstag; Brandenburg Gate; and Museum Island, including the Berliner Dom.
The majority of these seemingly old buildings were heavily damaged, if not completely destroyed, during the world wars and have been rebuilt or repaired to mirror their former image and glory - which gave the whole 'historical experience' a very new edge.