When you go to other city, especially Seoul, you can ride train or bus.
At Pyeongtaek station, there are many trains going to Yongsan station or Seoul station.
Or you can go Jijae station(1 subway station apart from Pyeongtaek station) and ride SRT.
It only takes about 20mins from Jijae to Suseo station. Suseo is one of the subway station in Seoul.

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