Who is said to have been President of The United States for one day? Where did he spent that day?

David Rice-Atchison and he spent the day in bed!

here

Yes, good answer Jenny.

Actually, I don't think that Atchison was president at all. Those who do say that his becoming president is a result of the President-elect not being inaugurated. In an inauguration, the incoming officer is sworn in. Atchison was never sworn in as president. However, the link to Wikipedia (above) correctly points out that taking the oath of office is not a requirement under the Constitution. Does this mean that Atchison was not required to be sworn in? If so, the the President-elect was also not required to be sworn in to take office. Thus, the same line of reasoning that Atchison's proponents say caused him to be president shows that the President-elect was President at the time.