Who Knew? is a collection of Cheddar's favorite explainers organized in episodes together by topic. This week, our host, Hana Ostapchuk, presents three stories on the evolution of the airline industry.

Tom Delgado takes you on a complete tour of the mansions of Millionaire's Row next to Central Park (aka Fifth Avenue). Millionaire's Row hit its peak in the mid to late 1800's and early 1900's as it went further north. He stops by the Carnegie Mansion, the Frick Mansion, and the Felix Warburg house, among others. Shot by Eric Thirteen.

Fort Tryon Park is a 66 acre park established in 1935 that sits at the Northern tip of Manhattan's Washington Heights neighborhood. In this vintage photograph of the area captured two decades prior, you can see the private C.K. Billings Estate along with its impressive arched pathway structure and massive mansion, sitting where The Met Cloisters sits today.

Here is a Google Street View of the same arched structure, seen from a different angle, as it appears now alongside the Henry Hudson Parkway.