Their 3rd nuclear test was on February 12, 2013 and had a suspected yield between 12-21 kt (similar to that of the bomb dropped on Hiroshima). The test was conducted underground in the northeast of the country and registered as a 5.1 magnitude earthquake. This test came a few months after a successful launch which the international community agrees was actually a long-range rocket test in the guise of a domestic satellite launch.
North Korea is one of the most militarized countries on Earth and the landscape is littered with military sties ranging from small outposts to massive secret bases. One of these bases is a missile test site, the Tonghae Satellite Launch Site, seems to be growing. It is located on the coast of the Sea of Japan (East Sea of Korea) and is surrounded by small villages and rugged terrain.
The site has multiple testing facilities and rocket stands. I seem to have found a new test stand in the process of construction. The image below shows you the site in 2010 (left) which is nothing but empty ground and the image on the right is from 2012. As you can clearly see, there is a large structure being built. The layout and design is indicative of a new test stand.
(click for larger image)
Coordinates: 40° 51' 29.47" N 129° 41' 11.56" E
Only time will tell what will happen with this new site, but if the past is any indicator North Korea is well on its way to advancing their missile technology with no signs of slowing down.