Off the typical tourist trail in Berlin, the German Resistance Memorial and Museum at Bendlerblock is an expansive building. On my recent visit I managed to spend a few hours learning about Germans who fought against the Third Reich before and during WWII, though typically the museum features exhibits throughout Germany's long history.
This free history museum highlights many of the unsung heroes, as well as more famous characters from WWII. A special exhibit on Claus von Stauffenberg, who famously came close to assassinating Hitler, was particularly interesting, though the real delight came in learning about individuals who don't get as much attention. Spend a few hours here and you'll come away with a mix of emotions—sad, hopeful, excited, inspired, and piqued.