Abstract
Cheongna City Tower is a 448-meter-high rise observatory tower with 8.7:1 aspect ratio located at central lake park in Incheon Cheongna international city. The tower is a crystal shaped image and it turns invisible when the façade is activated. The tower was planned to be hexagonal 30-story building with two basements which are composed of mega frame structure using mega column and mega brace. In order to minimize the wind effect, the blow-through area was installed so that the wind can pass through. This observatory tower is an unprecedented project since the whole building is covered by façade for invisibility effect.