If you are in Korea anywhere between late March and late October you must go to a baseball game at Jamsil Stadium (or Sajik Stadium in Busan, or Daegu Stadium in Daegu, or Munhak Stadium in Incheon.....you get the idea).
To reach Jamsil stadium take the Green Line (#2, called the outer circle line) and get off at "Sports Complex Station" and use "Exit 5" There are a number of line-up areas for tickets and the booths open up two hours before game time. Ticket prices range from 7000-12000KRW (slightly more on weekends) and game times are 5pm on weekends and 630pm on weeknights. There are no games on Monday.
I would suggest arriving between 430-500pm to ensure you get the seats you want. If you arrive later the only seats that will be available are usually general seating in the outfield, although that is usually a fun spot to be in.
The ideal tickets are between first or third base and their respective outfield foul poles. If you sit in this section you will be amongst the most dedicated and passionate fans (and you'll be closer to the cheerleaders!). I have been to all but one baseball stadium in Korea, and seen every team except for Hanwha, and I would say that Jamsil is a really nice setting for baseball, and there is always a game as Doosan Bears, Kia Tigers, and LG Twins all play there.
Doosan Bears has an english version of their website, and if you ask your hotel or guesthouse they will be able to look up the schedule in Korean and provide you with info.
The crowds are not only incredibly enthusiastic, but they will be appreciative of the fact that you have come to watch a game. Do not be surprised if you are offered food and drinks by those sitting around you as this is something that has happened to me at every game I have attended without fail.
Unlike North America, you can bring in your own food and drinks, and the areas outside the stadium are lined with tons of food choices.
Even if you are not a sports fan you must go to at least one game to experience something truly cultural in Korea
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC