If you've never heard of it, there's a maximum security prison in the Philippines where the prisoners have to DANCE as part of their rehabilitation.

You might remember them from the huge choreographed "Thriller" dance they did back in 2007.

This time, hundreds of them did the "Gangnam Style" dance . . . in the pouring RAIN.  The video was posted on YouTube over the weekend, and it already has over a million hits.

(It starts at :27.)