Hitler started building a monstrous 400,000-capacity stadium in Nuremberg.
Prior to construction, the architect [Albert Speer] had pointed out to the Nazi dictator that the measurements of “his” playing fields did not match official Olympic dimensions. But Hitler was unconcerned and retorted: “That’s totally unimportant. The 1940 Olympics will be taking place in Tokyo. But after that they will be held for all eternity in Germany – and in this stadium. And it is we who will determine how the sporting field is measured.” The plan was to have the German Stadium completed in time for the 1945 Reich Party Congress.
From Spiegel, h/t The Browser
Rungrado May Day Stadium, Pyongyang, with 150,000 capacity is presently the world’s largest, according to wikipedia.