Busan is a port city located in the south-eastern of South Korea. The KTX train that Seok-woo & Su-an took in Seoul was bound toward Busan.
History[]
The city was first mentioned in the titular film Train to Busan. Su-an wanted to see her mom there for her birthday.
When the virus first broke out, the Korean military established a quarantine zone near Busan, and began taking in as much refugees who were displaced in South Korea due to the virus as possible, including Su-an and Seong-kyeong. It's unknown if Su-an ever reunited with her mom.
However, their efforts of establishing a safe quarantine zone wasn't successful, due to the fact that everyone was evacuated there, which made it dangerous everywhere.