I’ve worked in the Flatiron building for about two and a half years. While this always impresses little kids (“That’s where Spider-Man works!”), it is a really normal office building on the inside. Except for the vintage mail chutes. They’ve been out of service for decades, of course. There are rumors that they found years of lost correspondence stuck in the chutes when they cleaned it out. The building management has wisely left the original details and mailing instructions. Check it out: a bit of old America inside an architectural landmark.