You know the story of Archimedes, right? According to legend, he was racking his brain trying to figure out a method for determining the volume of an object with an irregular shape. This was basically a homework assignment from King Hiero II. Archimedes was getting into the tub at the end of the day and he noticed that the level of the tub water rose when he got into the tub in correlation to his own body volume. Archimedes realized that he could use this method to determine the density of any object. He cried out "Eureka!" and ran naked through the streets, saving his job and giving us the great gift of Archimedes' principle.
And you know what? We still get our best ideas about physics, space and the nature of the universe while we're in the shower. Thanks, Archimedes. Eureka.