Actually there's a proper slum district in Bangkok...called Khlong Toey near Sukhumvit.
Although Klong Toei is one of the larger, and the most (in)famous, there are "slums" all over Bangkok and other Thai cities. Some of the more "interesting" are the little villages that pop up in vacant green belts.
Here is a shot taken from just south of Sathorn Road, near the river. For those familiar, Center Pointe Silom is just about center. This is some very expensive real estate. But, you still see "slums", very expensive "slums"!
The huge building, to the right, is a casualty of the '97 financial collapse. It was never finished and has stood vacant since then. As you can see, it is now used as a billboard.
It's a composite of 3 bracketed exposures. Otherwise, either the sky would be blown out, or the rest would be woefully underexposed.
One of the reasons so much of Bangkok appears "run down" is all the mold and mildew. It rains quite often and the extreme humidity keeps buildings from drying. Few people are inclined to try to clean it off; it's a never ending task.