In July 2016 I visited Lotte World Tower in the Seoul suburb of Jamsil. At that stage the building was complete (at 555 metres, currently the fifth highest building in the world) but still being fitted out, so the observation decks weren’t open, but a shopping mall at the base was open. It was officially opened last week, on the 3rd of April, preceded by a fireworks and laser display on the night of the 2nd.
News report about the fireworks (from YTN News)
My own photo