In The Summer I Turned Pretty season 3 finale, Conrad travels toward Brussels, Belgium.
The finale, “At Last,” premiered on September 17, 2025. Conrad visits Belly in Paris on his way to a conference in Brussels, giving the episode a second European destination beyond the main Paris setting.
After spending time with Belly, Conrad leaves for the train to Brussels. Belly realizes that she loves him and chases after the departing train to declare her feelings, leading to their reunion with a kiss.
Paris is where Conrad meets Belly, not the city he is traveling toward for the conference. Brussels is therefore the precise answer to the travel detail in the finale.