A massive Seoul underground mall is planned as part of a transit zone that will match Coex Mall in size.
One whole level of the development will feature retail and restaurants.
Comprising six underground floors, the Gangnam district complex in the south of the city will cover 160,000 sqm.
If Seoul manages to connect the complex with Coex Mall and a new shopping mall now being built by Hyundai Motor Group, the three areas will encompass a total 420,000 sqm.
City officials say that about 1.7 trillion won ($1.5 billion) will be allocated for the project, which is expected to serve more than 580,000 commuters daily. The funding will include private investment.
Seoul will come up with a master plan by the end of this month, wrap up administrative procedures by the end of this year and open public bidding for an architectural design early next year.
More than 50 metres deep, the sixth level will service six different rail lines, from subway to KTX bullet trains. Also, 90 bus routes will pass through the area, with the transit centre on the second level.
Because of a new high-speed train line, it will take only five minutes to travel from the complex to Seoul City Hall, now a one-hour journey.
Several Great Train Express (GTX) lines will pass through the underground transit zone, connecting Seoul with neighbouring cities in Gyeonggi.
City terminal services for Incheon International Airport, now provided at Coex, will probably be moved to the second basement floor of the new complex.