The interior of Il Duomo Florence has a unique clock prominently displayed on the back wall.
This clock was designed by Paolo Uccello, and is a twenty four hour model.
Paintings on the clock face represent four saints, all of whom were men.
This is an operational clock which accurately tells time, and the hands run backwards instead of in a clockwise direction.

Here is a link to a youtube video about the clock.
https://www.youtube.com/watch?v=oJmlfAIRILA