Starting to plan our first trip to Korea for later this year and wondering what is the Korean equivalent to Japan's SUICA card (multiple use pre-paid cards for subways + convenience stores?) If this exists, how much would you load on for a week in Seoul and 5 days in Busan, with plans to take trains around as much as possible. And is it possible to purchase in advance or does this need to be purchased on arrival? Thanks in advance for your help.