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The design is based on the original 'Henniger Turm', a grain storage silo for the nearby brewery with an observation deck/retaurant on top. Originally built in 1961, it was demolished in 2013. Due to the fact that it was one of the most well-known landmarks in Frankfurt, the developer of the residential highrise decided that the design of the new tower should be inspired by the old Henniger Turm, thus its rather unique shape.
The old Henniger Turm.
http://www.aviewoncities.com/img/fra...kvege3795s.jpg