The tunnels of the NYC subway system are dark and full of mystery.
This one in particular contains ‘bell mouths’ – which were usually built where a planned subway route was suppose to diverge from a route that was actually built. They were meant to allow for later construction of the planned route without disrupting the now existing, active tracks. Many many subway routes were planned all over NYC, and after WW2, nearly all of those planned routes were never even started.
The bell mouths of this tunnel are different though. They were meant to allow for the eventual reconstruction of a nearby local subway station into one that could accommodate both local and express trains via island platforms. This of course never took place, but the widened tunnel bell mouths remain.