The New York City subway carries many secrets, like any extensive system that was built over time. But it also comes with quite a bit of lore — from urban explorers who have explored every nook of its vastness, the technological feat it was to build in some of the toughest Manhattan schist, and its evolution from high-class experiment to mass ridership. As the subway is always changing, so will this list. We have just added more of our favorite secrets, from hidden art installations and remnants of the past, to fun facts about how the system works.

We encourage you to comment and Tweet at us (@untappedcities) with other hidden gems. Special thanks to Matt Litwack, author of Beneath the Streets: The Hidden Relics of New York’s Subway System, and Untapped Cities Chief Experience Officer Justin Rivers, for contributing their finds to this piece.