New York City is full of secrets. Or rather, lesser-known yet nonetheless fascinating stories and facts that have long existed in the shadow of more publicized events and places. And while these tidbits might be more obscure, they contribute to the energy, vibrancy, and culture that makes NYC the iconic place that it is. This year marks 400th birthday of the Big Apple, making it an ideal time to dig into and celebrate all of the city’s exciting history. Below, AD covers nine of New York City’s most thrilling secrets, including how it earned its “Big Apple” nickname, record-setting real estate transactions, and even covert train stations. How many of them did you already know?