There's multiple dungeons in the .dats already developed that they're not using. They could easily open one up and fill it full of mobs and chests like Sposhae. It doesn't have to be developed overnight, it's already done.
http://www.youtube.com/watch?v=c6UtlDJGDIk
http://www.youtube.com/watch?v=Ea7tB...eature=related
http://www.youtube.com/watch?v=uVpBB...eature=related