Underground in Seoul

After my mountainous adventure, I want to comment about how easy it was to journey into the countryside via Seoul's subway system:

I was able to leave the city to enter Bokhansan National Park, which is where the mountain I climbed is, via Seoul’s subway system. From there, a brief cab ride took me and four of my friends to the base of the mountain.
Seoul’s subway system is generally efficient. Riding the subway for a relatively short distance costs about 90 cents and the subway arrives at each stop every few minutes. The subway system sprawls outwards from the city center, allowing us to reach the outskirts of Seoul (and Bokhansan National Park) within an hour. The subway closes at about midnight each night, prompting some youth to spend the entire night in 24-hour-a-day cafes, bars, theatres or karaoke rooms until the subways begin service again at 5:30 a.m. A note about this: the subway will stop at whatever station it is currently located at; there is no “last route.”
I've caught a cab a few times here, but several of my friends have partied "Korean style" as they say and haven't returned home until the sun is rising.

I’ve met several New Yorkers who’ve vowed Seoul’s subways are quieter and cleaner than New York’s subway system. They’re also faster than Seattle’s bus system, which is obviously impeded by varying amounts of traffic. Also, riders here use a card to access the subway and the bus system. Transfers are recorded electronically so that one may emerge into the sunlight to catch a bus and need only scan the card again. Hence, no need for change and no need for paper. If you come to Seoul, buy the subway/metro card at the station. It is called “T-Money” and it will help you.