The roundabout surrounding the Arc de Triomphe in Paris. It might look beautiful from the air, but have 12 major avenues come togther in the same stop is not good for traffic!

International infrastructure is incredibly interesting, and can be just as distinct from US infrastructure are it is from US culture. Well, maybe not that distinct.

Aside from the obvious "they drive on the other side," each country has their own nuances for how they do their infrastructure, whether it's bike-based infrastructure in the Netherlands or the "Five Fingers" plan of Denmark. Even small details, like toll booths on freeways, can be extremely intriguing (to me, at least)!