This mid-block, low-rise office building just off Park Avenue South is a lesser-known work by those giants of mid-century architecture Skidmore Owings and Merrill. As the New York Landmarks Preservation Commission website states (the annex was landmarked in 2008), the complex is more unique for being a low-rise mid-century office building in Manhattan. It was originally designed in 1959 but not completed until 1963 and constructed as the Guardian Life Insurance Annex to the grand Guardian Life headquarters next door (now the W Union Square). Much more about this building can be read in its designation report here. The main entrance is on East 17th Street but the building goes through the block as seen below on East 18th Street.