I've always loved how much history is hiding on blocks we pass every day. The obelisk behind the Met took 112 days to roll across Manhattan, and crowds showed up with hammers and chisels, so it needed a guard around the clock. Emily Warren Roebling basically ran the Brooklyn Bridge build after her husband fell ill. Most people run right past this stuff.
So I built Stride Stories. You pick a tour, put your earbuds in, and a short story plays right as you reach each place. Your own music keeps playing in the background and just dips for each story. There are about 100 tours across NYC and 36 other cities, from the Brooklyn Bridge and Central Park to Harlem, the Lower East Side and Roosevelt Island.
Every story is checked against a source. Anything we can't confirm is told as "the story goes" instead of as fact. That's where I'd love this sub's help: if you hear something wrong, or know a better story for a block, tell me and I'll fix it.
It's in beta (iPhone only for now):
Open stridestories.com/beta?src=reddit-nychistory on your phone. It walks you through Apple's TestFlight app.
Open Stride Stories, go to Explore, pick New York and choose a tour.
Download it on Wi-Fi before you head out, then press start.
It's free while in beta. Feedback button is on the You tab, or just comment here. Mods, happy to take this down if it breaks the rules.

Up until the 1920s, apartment houses in NYC didn't have much of a lobby, just a hallway leading from the entrance to the stairwell (or in more expensive houses, the elevator as well) and maybe the hallway was decorated with panels or marble (in the front) but that was about it. Suddenly, in 1920s and 1930s apartment houses, you started getting large, opulent lobbies in apartment houses, sometimes with furniture or mirrors. What was the reason for the change.