Instead of paying top dollar to the observation deck, consider other public parts of the building that may be lower, but still offer lovely views of the city. Try the food court on the 31st floor, which requires getting a security pass at reception first.
Further up, the Signiel Hotel occupies the 76th to 101st floors.
The skyscraper's shadow reaches far eastwards.
Gangnam was against the light so looked a bit blurry at this time of the afternoon.