Palace of Soviets, Moscow

Design: Boris Iofan, Vladimir Shchuko and Vladimir Gelfreikh
If built, it would have become the world's tallest structure (420 m). Construction started in 1937, and was terminated by the German invasion in 1941. In 1941-1942, its steel frame was disassembled for use in fortifications and bridges. Construction has never been resumed.

Read about it (Wiki, EN)
Sketch © МУАР