What building did Mies van der Rohe first envision as an all-glass skyscraper in 1920?

Mies van der Rohe first envisioned the Mile High Tower as an all-glass skyscraper in 1920. This design marked a significant milestone in architectural history, demonstrating his innovative use of glass to create transparency and lightness in high-rise structures. The concept embodied Mies' vision of modern architecture, emphasizing simplicity, functionality, and the relationship between indoor and outdoor spaces.

The idea of using glass extensively was revolutionary at the time and set the stage for many of his later works, including the Seagram Building, which successfully combined modern materials with an elegant aesthetic. This earlier vision contributed significantly to the development of skyscraper design, influencing other architects and shaping the modern skyline.

The other choices, although significant in Mies' career, did not represent his initial ideas for an all-glass skyscraper during that specific timeframe.