T-money is a pre-paid card used for public transportation in Seoul.
It can be used for both buses and subways.
How to use
Place the T-money card to the card-reader.
The display will tell you how much has been deducted from your card
and your current balance.
By using a T-money card, you will enjoy greater discount benefits
than with cash.
The base transit fare for a T-money card user is 800 KRW (vs. 900 KRW if
you pay cash)
T-money card offers transfer discounts when transferring from
bus to bus, bus to subway, or vice-versa.
Just remember to touch your T-money card to the card-reader
whenever you get on and off.
How to buy/recharge/refund
The card itself costs 2,500 KRW, and afterwards one can "recharge" the card
when necessary (The card has initially no money).
T-money can be recharged in subway stations, either automatically or by the
person working behind the counter.
Other places to buy/recharge/refund it include many sidewalk newspaper vendors,
convenience stores (GS25), and other places where the T-money sign is shown.
When departing Seoul, you can get a refund for any remaining amount on the card
at a T-money card vendor.