Now we have the Korean Demilitarized Zone, also known as the DMZ. The DMZ is a very long stretch of land that cuts right across and divides Korea into its Northern and Southern parts. It is a 250km long and 4km wide path that is constantly under watch. The border is closed and because of this, it means that no one is allowed to cross, it is so heavily guarded in fact that casualties have occurred on either end by people trying to cross.
The only way to get from North to South Korea or vice versa, would be to travel to an intermittent country such as Russia and then go to your desired destination. It’s a shame that tensions are so high, but hopefully there is a brighter future where it may be safe to cross.