https://www.nycsubway.org/wiki/New_York_City_Subway_Track_Maps
This site is cool. It shows you maps of subway tracks (not route maps but track maps) in Manhattan, The Bronx, Queens, and Brooklyn. I love that we are able to have a peek at what goes beyond our sightline while on the subway platform.
For example, the map below shows how tracks are laid out in the East Village/Lower East Side. You’ll have to click on the picture to see it in good detail:
If only we could take guided tours of abandoned rail lines!