Conrad is traveling to Brussels for a conference when he visits Belly in The Summer I Turned Pretty season 3’s finale.
In episode 11, “At Last,” Conrad goes to Paris to meet Belly on her 22nd birthday. His visit is connected to a professional trip: he is on his way to a conference in Brussels and must eventually leave Paris to continue the journey by train.
The Brussels detail helps explain why the reunion has a time limit. Conrad and Belly spend the day together, attend her birthday dinner, and discuss their past, but Conrad still plans to continue to the conference. Belly realizes what she wants only after he has departed and runs after him.
Paris is the location of their meeting, not the conference destination. This distinction is a common source of confusion because the finale’s central setting is Belly’s Paris life, while Brussels appears as Conrad’s next stop.