Fontainebleau, France
A six-month exchange taken entirely in French, which is where the fluency came from. Doing coursework in a second language taught me how much of engineering is communication — when you cannot rely on saying it fluently, you learn to check that you have actually been understood, and to ask rather than assume. It also made me a lot more comfortable being the person in the room who does not yet know how things work.
Where this was, on the map