Tomasz Nguyen X.
Google
It's not easy to find, taking into account the numerous narrow pedestrian alleys, but once you get there, you realised it was really worth it. It's actually impressive how the Arc managed to be intact through the ages until now. And how it became a part of a modern city of Triest. They're are more hidden gems as this one located around the city centre. Take time to stroll around and I'm sure you'll find them.