It turns out that Seoul is only about 40 km from North Korea.

Humm.... should I be worried about that?
:)
Actually, good 'ole mom and dad do enough worrying for me.

It's intriguing, though. That area has been through so much war and has had such a violent history. The man they call Kim Jung Il is no less offensive than the brutal Chinese invasions or Japanese colonizations.
Oh, and don't forget the America war. Where communism and oil are involved, you can guarantee that we'll be there.... waging our (ulterior motive-driven) moral war.
But the repression, starvation, and opposable thumb that has squished the life right out of millions (some say the population of North Korea is less than half what it used to be) simply continues to add to a brutal history.

As an American tourist, I would have a very hard time getting into North Korea. Nor would I really want to since all your actions are controlled and restricted by, not one, but two mandatory tour guides. It's expensive and not in any way a "cultural" experience.
But, I can experience a trip to the DMZ to view the border, some government buildings, and an extensive tunnel system. Apparently, you can hear the propoganda blaring from loud speakers just over the border. It plays for 12 hours a day. Geez.
And I think you have to sign a disclaimer saying that you understand the risks (of stray bullets and such). No big deal. I guarantee that visiting the border of North Korea is safer than driving for 30 minutes on a Houston freeway.