From Nanjing East Road Taipei Metro to Shungshan airport, fly to Seoul Gimpo airport, then train to Seoul. 4 h 47 min $263. From Taipei train to Taoyuan HSR Station, Taoyuan Metro to Taipei airport, fly to Seoul airport, then train to Seoul. 6 h 4 min $211.
Flights from Taipei to Seoul
T'way Air, China Airlines and 3 other airlines fly from Taipei to Seoul 3 times a day.