Post-graduate courses at the local universities?

Depending what you want to study, there are plenty of subjects to study. The Vietnamese are very industrious so there is no shortage of courses catering to all needs.
The most relevant for you may be to improve your English. Check out classes like "ILA Jumpstart Certificate in English - Level 1A" .

Joking aside, there are MBA programs which require same qualification as US universities: GMAT, TOEFL, undergrad degree, experience,.
They are not cheap though and their quality really varies.

RMIT offers different courses. The best English based state universities do take foreign students but I doubt they'll take you.
https://www.hcmiu.edu.vn/Admission.aspx

If you just want to challenge your brain, there are plenty of international professional certification programs which you just read at home and turn up for the exam. Among the Vietnamese elite students, the CFA program is popular mostly for its demanding workload. Exam once year in Hanoi, and SGN (as well as around over 100 cities around the world).
http://www.cfainstitute.org/cfaprogram/ … index.aspx
Full disclosure, yours truly is one of 40-50 in Vietnam who managed to survive the tests.

Seriously, I'd just take a new language course, say Chinese, if I were you. Otherwise, just take some of the night courses in the local universities aimed at working adults. There is no qualification required for the courses I checked.

Anatta,

Chinese?  You must be out of your mind!    Don't you know how hard that is???  I took a stab at it back in college...  Lasted only one session!  I dropped it so fast, in favor of Spanish, that the professor didn't even get a chance to know my name.

Plus, I speak Vietnamese; and there are quite a few Vietnamese who speak Chinese here.  So, there is no need for me to revisit that fiasco. 

I would really like to try my hands at Vietnamese law.  But so far, among all of the people I talked to in Can Tho, the school requires Party membership...  No can do that, Senior.    Its student body consists of mostly military or police officers. 

Or Vietnamese history...  I think that is very interesting topic to dwell into.  But, my concern is whether they are going to accept my American education, or are they going to put me in 6th grade history...  That will be worst than dealing with you and Budman.

As I said, if it is just to challenge your brain, just buy the books and read them yourself. That is how I learned the Vietnamese laws. They are quite simple actually, not as complicated or advanced as, say, US laws.

As opposed to the common law system as US law system where case precedent is important, Vietnamese law is civil law based, i.e., strict interpretation of wordings of the laws (at least in principle), so it is just about reading the laws and learn how to interpret them. Studying US laws requires you to learn about relevant cases in different courts as well thus much more difficult.