Main Tower is a 56-storey, 200 m (656 ft) skyscraper in the Innenstadt district of Frankfurt, Germany. It is named after the nearby Main river. The building is 240 m (787 ft) when its antenna spire is included. The tower has five underground floors and two public viewing platforms. It is the only skyscraper in Frankfurt with a public viewing observatory. It is the 4th tallest building in Frankfurt and the 4th tallest in Germany, tied with Tower 185. The foyer of the building has two art pieces accessible to the public: the video installation by Bill Viola "The World of Appearances" and the wall mosaic by Stephan Huber "Frankfurter Treppe / XX. Jahrhundert" (English: "Frankfurt's Steps/20th century"). The tower's design features what appears to be two connected towers. The smaller of the two is of a cuboid shape and a design common to 1970s architecture. The second and taller of the two towers is a circular tower with an entire blue glass exterior which features the transmission tower on top.