Bicycles on trains?

If you were thinking of trains in Switzerland or the Nethelands, then too bad, you won't find any.

If you have a folding bike, e.g. Brompton, then you might be able to put them in the luggage compartment on KTX trains. The same cannot be said of Mugunghwa and Saemaul trains, since there are different types of passenger cars being operated under the same class name. Not quite sure about the measurement of overhead luggage shelves, but you wouldn't want to store your bike over your or somebody else's head, would you?

I'll take that as a 'no'.

I don't know about regular trains, but . . .

Seoul started a test program in October where people can take their bikes (regular, not folded) on the subway on Sundays, though you are supposed to only board the first or last cars. Some of those 1st/last cars have had some seats removed and metal rails installed.

I transported a bike one Sunday last month and had no problems.

The idea is that the program may be expanded in the future, as Seoul has "promised" to become more bike-friendly.