This report from 2002 provides some insight on the red light districts of Seoul like 588, Hooker Hill and Itaewon as well as the freelancer pick up hot spot Hollywoods. However, a lot of things have changed since then.
Fun with Korean pussy and Korean Escorts as prostitution in South Korea is available inside red-light districts like Hooker Hill for locals and there is a large freelancer scene for foreign expats and sex tourists.