Never thought I'd be able to add my insight on this topic on Enworld, but here goes:
Living in Korea now, and have for almost a decade. My wife (now Korean-American) is a descendant of King SeJong, the "greatest" of the Korean Kings. He created the language Hangul in the 1400's to replace the Chinese borrowed language - they used many of the characters/pictures used in chinese, although with different pronunciations and often altered meanings. It was a very difficult language and created a distinct class of educated scholars (very few) and the masses.
Sejong created a scientific language that would be easy to learn. It is, extremely. [learning the Korean language is another thing altogether]. With 5 hours study, you could read any Korea word, promised.
Side note: being a direct decedent of the King means nothing these days, however it is pretty cool for my D&D loving 9 year old son. When we visit Seoul we always visit the Sejong family palace -
GyeongBokGung Palace. It's enormous, mysterious, and filled with adventure for anyone, but especially a young mind like my son. He likes to mention that hereditarily, this is also his palace... though I doubt they'd look too kindly on a 1/2 Korean 1/2 Caucasian descendant.
This card is likely not about sex mostly b/c it is for men and women. It is in Korea, and the 20,000 won equals about $17.
You can find cards like this littering the streets in downtown areas late at night, especially on the weekend. Daily you can see drop-out boys riding their mopeds flipping business cards (for all sorts of business, but heavy on the nightclub and hostess clubs) in all directions. Probably in Korean Town LA as well. In Japan, where sex is famously more open, it'll look like sex cards fell from the sky like snow. (none of this, especially in Korea, will help a desperate foreigner find quick sex by the way - these places generally aren't too interested in foreign clients).
Many massage parlors are not open 24 hrs. If it's open 24 hours, it does have a greater chance to be a pseudo-sex shop. You could still go to these places and get the straight massage, but if you paid more, and only if the masseuse was willing, there could be a deal made between both parties.
The business of sex is huge in Korea, from hostess karaoke clubs, coffee shop girls who deliver coffee and ride around on mopeds, salons that do more than wash your hair, to the dingy small alleys where sad ladies stand in floor to ceiling storefront windows drenched in red lights. It is much more accepted here than in America. However, sex here is not in your face, is not the seedy swampland at all you'll find in places like Thailand. Rather it is understood that sex happens and you might as well make money from it, although it is always hidden and behind doors. In general Korea is a *very* modest country and think Americans are sluts. Odd, but possibly true. The only big problem I have with it is that this is semi-approved for men, while women seeking such places would be considered absolutely wretched.
The sex industry is huge - these articles say it ranges from 1-5% of Gross Domestic Product, which is nuts - and you should know that Korea is very wealthy, 15th GNP in the world.
Commercial sex survives despite crackdown
4%
wiki never lies
As for baths, salons, etc, they are everywhere. I lived for a year in an apt with no shower. I went every other day to the small public bath down the block. They are awesome. My sons and I go monthly. I've gone with the male members of my wife's family. About 10 of us from three generations sitting around naked soaking then scrubbing ourselves to get rid of the dead skin. Odd, but with the proper mindset, a very healthy thing. When my dad visited, he would have none of it, not surprisingly.
But as for D&D, I think it's an awesome idea. Drop a card on a dead person's body or a sort of coupon in a treasure chest. What will it lead to? Sex? "Saw"-type execution club? Magic trade show? Spy or assassin's calling card, etc.