One Hundred Eleven - "Architecturally Yours". . .

There are two sets of spiral staircases in the U. S. Supreme Court Building. They are free-standing and made of marble. Unfortunately, the only view you get is of one of them and that is limited to a cordoned off area about two feet by two feet. You had to be a contortionist to get any picture of it at all! Mike Di knows his DC landmarks with several others offering great guesses.

So on to #111 - there is a castle, this castle on the Mall in DC. We know it is not home to any royalty. What is it's function???

FYI - its interior architecture is as impressive as what is inside.