Has to be the week long Germany trip in high school. Our class was approached by the local theater and asked to be the amateur representatives on a drama exchange in Frankfurt an der Oder called "Love in Europe". I should mention we were all drama majors, lol. There were a bunch of different countries participating, and each sent both a professional and an amateur delegation.
I remember getting along well with the group from Ireland, spending more time with them than anyone else (I didn't get very well along with my class in general, having been picked as the black sheep of the class). There were workshops, performances by all of the delegations, a separate day for the amateurs and the professionals and just generally a lot of mingling.
Have a very fond memory of making one of the women from our own professional delegation (who's now one of the more famous actresses in the country - but at the time she was just on the cusp of transitioning from theater work to television/movies) almost spill her wine in surprise when I switched back to speaking Norwegian (since I was hanging out with the Irish group mostly, lol). For some reason, if you're abroad and reveal yourself to be a fellow Norwegian you get extra popular, lol.