>> chung min lee: that's it. >> whitaker: i'm in the hands of north korea? et's stay on this side. it was all surreal. to seoul had the feel of a cold war theme park-- complete with a fake village on the north korean side built to impress the south. and in case you missed the point, loudspeakers blared propaganda: marshal songs praising kim jong-un. a few miles away, tourists crowded an observation deck, snapping photos with troops, cardboard cut-outs, and the real ones. what the visitors could not see on the other side of those mountains are 10,000 artillery pieces the north korean military has aimed at seoul. all of which could reach the 28 million people in and around the south korean capital. u.s. war planners estimate 500,000 people could be killed in a second korean war. is there any other metropolitan area on earth this vulnerable? >> james slife: certainly nothing that approaches seoul in terms of the size, the density of the population. there's nothing like it. >> whitaker: u.s. air force general james slife flew with us over the city. it's just 30 m