Citigroup Center is one of Midtown's more distinctive skyscrapers, easy to spot by its slanted roof and tall base columns. It is mainly an architecture stop rather than a long visit, but the building has enough oddness and engineering history to reward a look.
The public atrium is the useful part for travellers: step inside while walking between Grand Central, MoMA, and the east side of Midtown. The building works best as a quick architectural detour rather than a destination that fills an afternoon.