Mills Hotel, 1907. Around the turn of the 20th century, banker and philanthropist Darius Ogden Mills had the idea to build residential hotels for single working men. The structure on 36th Street was the final of three hotels built and the largest. Completed in 1907, Ernest Flagg designed the 16-story, neo-Renaissance building. Flagg had written a landmark article in 1896 which decried the problems with the then-standard dumbbell layout of tenement housing. His plans for a "light-court tenement" involved less wall enclosure and greater room space, light, ventilation, and fire protection. After two successful Mills Hotels designed by Flagg, Mills commissioned a final one (though he hired the firm of Copeland & Dole, not Flagg). The building continued to serve as a home for single working men through the 1940s. In 1954 new owners renovated the building in a new, traditional hotel called the Keystone. Later in the 1980s, the building was retrofitted for offices and showrooms and parking lot on the first floor!