Seoul is menaced by Nork artillery in hardened positions in mountains north of the city. While cruise missile are fashionable, there is a far better way of neutralizing this threat that is fairly low tech, not terribly expensive, and devastating in its impact as counter battery fire.
16 inch naval guns.
Seoul could build several nondescript but impressively hardened concrete buildings in the city that would operate much like the turret of a battleship. Its ammo and propellant would be stored safely underground, but when needed, would rise on an elevator to be loaded into the gun. The false walls of the upper two floors would fall away, and all downrange targets could be pre-targeted.
The advantages of doing so are impressive. Not only with range far greater than the Nork guns, but if properly done, a single round could take out more than one hardened target, perhaps three or four.
Once firing, until the gun ran out of ammo, it would be extremely hard to take out, and could be used against a multitude of targets, devastating any Nork approach on the city.
Seoul could build several nondescript but impressively hardened concrete buildings in the city that would operate much like the turret of a battleship.
Stationary targets are very vulnerable. Even impressively armored turrets could be jammed by a direct hit, even if it doesn't penetrate the armor. On the other hand South Korea has a well developed rail network. A few strategically placed sidings and big rail guns could come into their own. The Krupp K5 had a range of 40 miles. Almost twice that of the 16" guns on the Iowa class. Largely due to its high angel mount.
Then there was the old Atomic Annie. Basically a road mobile rail gun. But the new guns would need to be placed out of range of the NK return fire. As soon as you pull the lanyard they know where you are. So your super heavy guns need to have a longer range then what they are using for counter battery fire.
