There is nothing at the farthest point from Seoul

For any point on Earth, the "farthest place" is already decided. Draw a straight line through that point and through the centre of the planet, and where it surfaces on the other side is the antipode. Calculate Seoul's antipode and you get this.

37.5665° S, 53.0220° W

There is no land there

Plot those coordinates on a world map and you land in the middle of the South Atlantic. Well past the waters off Uruguay, hundreds of kilometres from the nearest coast.

It looks like an anticlimax, but it is what the odds predict. About 70% of the Earth's surface is ocean, and the land is bunched into the northern hemisphere. Most antipodes of northern land fall into southern water. A city sitting at 37°N, like Seoul, is unlikely to have an antipode on land.

The distance from Seoul to that point is 20,015km. That is not an incidental number — it is the largest distance the Earth can produce. The planet's circumference is 40,030km, so this is exactly half of it, and the antipode is the same distance away whichever way you set off. East, west, or straight over the North Pole: it makes no difference.

So what is the farthest city you could actually reach

Line up the 366 cities in CouchColumbus's dictionary by distance from Seoul and the top of the list looks like this.

City	Country	From Seoul	From the antipode
Montevideo	Uruguay	19,606km	409km
Buenos Aires	Argentina	19,432km	583km
Puerto Iguazú	Argentina	18,676km	1,339km
Asunción	Paraguay	18,581km	1,434km
Santiago	Chile	18,356km	1,659km

First place is Montevideo, 19,606km from Seoul. With only 409km left to the antipode, calling it the farthest city on Earth from Seoul is not much of a stretch.

What stands out is that the whole top of the list is the east coast of South America. Uruguay, Argentina, Paraguay and Brazil come up one after another. Obvious enough once you know Seoul's antipode sits just offshore there, but not an order you would guess from a map. Ask someone for somewhere "far away" and they tend to say South Africa or New Zealand. Neither is on this list.

The other end

In the same dictionary, the closest city to Seoul is Incheon, at 27km. After that come Chuncheon at 75km, Daejeon at 140km, Sokcho at 159km and Gangneung at 168km.

From Incheon to Montevideo: 27km against 19,606km. A factor of 726. That is the spread between two entries in the same list.

Why bother working this out

This calculation is exactly what the service uses to pick waypoints. For each candidate city it divides the distance "origin → that city → destination" by the direct distance to get a detour ratio.

Put Montevideo on a Seoul-to-Jeju trip and the ratio comes out at 86. Eighty-six times the direct route. There was a time when the limit was simply dropped whenever candidates ran short, and an itinerary like that could genuinely be generated. Now it is cut off at 3.2.

Knowing where the farthest place is has nothing to do with going there. It is about not accidentally being sent there.