Aerogel, also know as frozen smoke, is the world’s lowest density solid, clocking in at 96% air. If you hold a small piece in your hand, it’s practically impossible to either see or feel, but if you poke it, it’s like styrofoam. It supports up to 4,000 times its own weight and can withstand a direct blast from two pounds of dynamite. It’s also the best insulator in existence.
Book Burning Memorial - In the center of Bebelplatz, a glass window showing rows and rows of empty bookshelves. The memorial commemorates the night in 1933 when 20,000 "anti-German" books were burned. There's a plaque nearby that says "Where they burn books, they will also burn humans in the end." Powerful.