如果唔搭ｆｌｙ機，點去韓國？

Take the train to China and then to the port 天津. In 天津 take a ferry to the port 仁川 in Korea. From 仁川 take the subway to Seoul.

香港 --> 北京--> 中國天津 (2~3 days, ~HK$600)
中國天津 --> 韓國仁川 (10 hours, ~HK$700)
仁川 --> Seoul (2 hours, HK$16)

The trip will take ~ 5 days because it takes time in transferring from one public transport to another. The total cost is around HK$1400, i.e. return trip for HK$2800.
You better buy a return ticket and fly to Korea becasue you will save time and money. You can get a return ticket to Seoul at ~HK$2000.

點解係[性教育]問題既?

搭船或搭火车再转船