Sports, huh? Not my strong point, but I can help.
Where's a good place to play volleyball in Seoul?
While it certainly appears to be a concrete jungle, there are a lot of sports facilities dispersed all around Seoul. You can find a basketball goal or a soccer field at just about every school in town and there are also dozens of non-Hangang parks that offer such facilities. However, it seems that the greatest concentration of sports facilities are located around the Han River in designated riverside green areas called Hangang Riverside Park.
The Hangang parks are hit or miss. Sometimes you can go there and no one will be on the field or court, but other times they might be booked for weeks ahead of time. For volleyball you can head to Gwangnaru, Jamsil, Jamwon, Banpo, Ichon, Yeouido, Yanghwa, Mangwon, Nanji. They all have some sort of facilities that should be okay for what you're looking for. I can't say which one is the best though. Korea hosted the third leg of the Women’s Beach Volleyball World Tour in 2008, so I can only assume that some of the courts are decent. They've invested a lot of dough in it as well.
If you're looking for indoor volleyball, then it might be a little harder. Like many baseball fields and basketball courts, it will require reserving a court for several months and paying a pretty hefty fee. Of course, that fee would be reduced if you got a big group together and split it, but then you have to deal with the issue of getting a big enough group together.
As I said, I'm not the biggest exercises guy, but I don't mind getting out there every once in awhile if there's the promise of a little barbecue and beer afterwards. I've never seen a shortage of places to enjoy the day and get in a little something for your health, so I good luck and happy hunting.
If your in the mood for some other sports and recreation facilities, check out this site.
Contributer and expat extrondinare, OpenMicah says...
For any public school or university teachers out there, one thing I would say is to check with the faculty at your school. Usually public schools have inter-school volleyball leagues some time in the fall, and teachers from one school usually play teachers from another school. I bet the teachers who play on your school volleyball team (especially the men) play occasionally with their buddies somewhere else out side of school and wouldn't mind you coming along.
I also would check with any foreigner or Korean friends you know working for a Korean company. They might actually have a company volleyball team that rents out a court once a week for a few hours. I had a friend working at a company, and all the guys in the office played basketball once a week on a rented court. He invited me and I split the cost with them. With 20 guys, it was only 20,000W a month. It wasn't competitive play or anything, but it was probably the only cheap way to play sports indoors. In the winter, especially.
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