I took two days a few weekends apart to walk the TriBeCa neighborhood, adding 11 miles to the tally.

 Two days' walk (everything inside the red line)

Two days' walk (everything inside the red line)

TriBeCa ("TRIangle BElow CAnal") is bounded by Canal St. to the north, West St. to the (you guessed it) west, Broadway to the east and Vesey St. to the south.  This obviously forms more of a trapezoid than a triangle, but who's counting?

The area evolved from farmland and residential neighborhoods to a commercial center in the mid-1800s.  Many of the warehouses and storefronts that were built during this period are still there today - some show their age but most have been beautifully restored.  

As the manufacturing economy exited New York (and in the US in general) after WWII, the neighborhood went through a period of decline.  It was famously described as a "demilitarized zone" by Harold Ramis in Ghostbusters in 1984, but by then the tide had already started to turn.  The vacant commercial space had attracted artists (long on talent but short on cash) and it wasn't long before the dilapidated warehouses were renovated and converted into trendy apartments and lofts.

The World Trade Center complex makes up the southern boundary of TriBeCa and the neighborhood (along with the rest of lower Manhattan) suffered financially after 9/11 due to a general loss of vitality.  Partially in response to this, Robert De Niro founded the Tribeca Film Festival in 2002 to contribute to the neighborhood's recovery and showcase lower Manhattan.  It must have done the trick, because today TriBeCa is neck and neck with SoHo for the title of "Most Expensive Neighborhood in New York".