Prostitution is everywhere in
South Korea, and takes a variety of forms.
The first form is the red light district. Any Korean city of respectable size will have one, usually close to downtown. It'll consist of a block or two packed with brothels, with hot Korean girls in short skirts hanging around outside. Inside, it's like a noraebang (singing room), except there's a hostess who'll bring out a bunch of girls and get you to each pick one (going to sleep with prostitutes is a group activity for Korean men). Then you order a case of beer for about 100,000 Won, drink it with the girls, and fool around with them there. Later, you can take them to one of the many motels nearby. The price of the girls is included with the beer, I believe.
Any Korean city, even the small towns, will also have "private bars", or "room salons". These are bars where you'll get a private room and a hostess to pour your drinks for you, and, for an additional fee, have sex with you.
Another thing you'll see in Korea is guys on scooters driving around with girls in short skirts riding side saddle on the back. These are "coffee girls". Their job is to deliver "coffee" to businessmen. In short, there are certain coffee shops you can call and order coffee to be brought to your home/workplace. You will in fact get coffee, but it will be delivered by a girl who is, essentially, a prostitute.
Perhaps the strangest form, however, is the "I-yong-won". These appear, to the untrained foreigner's eye, to be barber shops. They are distinguished from the normal kind by the presence of two red, white and blue barber poles out front. If you go in there, you can in fact get your hair cut, but there is one barber chair in the corner which has a screen, similar to a shower curtain that can be pulled around it. If you sit down in that one, you will be attended to by a woman who will do more than just cut your hair. The amazing thing about these places is that they are everywhere. There is usually one every three blocks or so; there is one right across the street from my school, in fact.
There are also a large number of Russian women who come to Korea as prostitutes, since many Korean men are interested in foreign women. Busan has a particularly large Russian population; the Russian women in that city turn their tricks in an area that used to be known as Texas Street around the time of the Korean War, but has subsequently been effectively turned into Russia Town.
Disclaimer: Although I have lived in Korea for a year now, I have not actually used any of the above services, although I have been to one of the brothels (see February 7, 2003)... I just didn't sleep with the prostitute. All this information (except for the stuff about the brothels) is second hand, told to me by Koreans, and other, more experienced foreigners. Therefore, some minor details may be a bit off, but the information is, on the whole, accurate.