Seoul can be reached from almost all international airports in India. That being said, there are no direct flights, with all flights having one or two stopovers along the way. Many flights from smaller airports first change at New Delhi itself. Airlines providing services from India to Seoul include China Eastern, Thai Airways, Malaysian Airlines, Shandong and a few others.
Seoul has two international airports. The Incheon International Airport Serves as the main airport, with international flights from all major countries. The Gimpo international airport serves as mostly a domestic airport, but has international flights from nearby Japan, Taiwan, and Shanghai and Beijing in China.
South Korea has very well made highways and expressways. Reaching Seoul via car is easy, since you will find expressways and highways heading to Seoul from almost anywhere.
Seoul is accessible by rail from anywhere in the country. Not just that, almost all major South Korean cities are connected to Seoul via the KTX high speed train. There are mainly 4 railway stations running the rail routes.
Seoul has 5 bus stations, each having buses covering different directions of South Korea. Bus connectivity of Seoul with the rest of the country is very efficient.
Individual ferry services connect South Korea to various ports in China from Incheon. South Korea is also on the route of a ferry that travels from Vladivostok in Russia to Sakaiminato in Japan, stopping at Donhae in South Korea in between.