Yes, Puddin; thanks for the reminder.
Slowhatch's floor plan
works well enough! While Banciao's connection between the train and subway lines is on the ground floor and B1, Taipei Main Station's connection hall is on B3, one floor below the rail lines on B2. This means TK and Rachel are boarding a high-speed train from the terminus station
of Taipei, and are definitely leaving the city for the south.
But where to? It's got to be far enough, at least beyond Hsinchu, to make the trip worthwhile... (Buses and local trains cover that distance just as easily.)