Kärntner Str. 1-3, 1010 Wien, Austria
One of the hidden gems of Vienna, Stock im Eisen is a midsection of a nail-tree from the Middle Ages. The oldest such tree in the world, this tree is behind glass in Stephansplatz.
It is called a nail-tree because there are old nails hammered into it. It is believed that smiths would practice hammering nail in the tree.