The Last Supper

I think you have to really see this in person to appreciate it. It's a mosaic of da Vinci's The Last Supper. This is what Wikipedia says about it:

There is a life-sized copy of Leonardo da Vinci's The Last Supper on the church's northern wall. It is a mosaic made by the Roman mosaic artist Giacomo Raffaelli which was ordered by Napoleon I in 1809, but it was not finished before Napoleon's abdication. Francis II of Austria bought it, wanting to install it in the Belvedere in Vienna. As it was too large for the building, it was set up on the north wall of the church, where it remains to this day. The mosaic is 9.18 x 4.47 m and weight approximatively 20 tons. (http://en.wikipedia.org/wiki/Minoritenkirche,_Vienna)

If you look at the photo on Wikipedia, you can actually see some of the detail of the individual tiles.