Night time is when South Korean cities come to life, during the day most of the cities look pretty similar and you have to look pretty hard to find buildings over 30 – 40 years old. The exception is central Seoul where there are some fantastic palaces and temples. The Sungnyemun (Namdaemun) Gate was burnt down by an arsonist in 2008 and restoration work was completed in April 2013. The best time to isolate the gate from the buildings around and the constant traffic which flows around the gate is nighttime by using long exposure a feature can be made of the traffic streams as the gateway is still the principal entrance into central Seoul.
Last time I was in Korea, I also spent some time in Deagu which is a great city, for the first time I had a hotel with views over the city so got the chance to take some images from the hotel. Taking images from high buildings is tricky unless you have access to the rooftop which is rare, most tall buildings do not for safety reasons have windows that open so you are left to take images through available windows but then there are problems at night because it is not always possible to turn off all of the lights especially in corridors or public access areas. For that reason I alway carry in my camera bag a square of black out cloth which has a hole cut from the centre through which the camera lens can be put to remove reflections.