A train of mining carts and a new structure are seen at the West Portal spoil pile at the Punggye-ri Nuclear Test Site in North Korea on April 20. (DigitalGlobe/38 North/Getty Images)In upcoming talks between the United States and North Korea, one of the key details is a mystery at a 7,200-foot-high point in the country's north: Mount Mantap. This mountain hosts part of a facility, Punggye-ri, that has been the site of all six of North Korea's nuclear weapons tests. However, his team is not the only one expressing worry about the structural integrity of Mount Mantap. Most analysts are forced to rely heavily on commercial satellite imagery when assessing Mount Mantap and Punggye-ri.

Source: Washington Post April 25, 2018 15:08 UTC