Unda Da Sea!
The MTA has gone through tons of train-car renovations over the course of it's 100-plus-year existence. That's a lot of train cars. What happens to them? Well, that may surprise you. The MTA strips them of parts, ships said parts to Staten Island, and then takes the shell of the car itself, and sinks it as marine habitats for under-sea creatures. But this isn't just in NYC... the MTA train cars span from Georgia to Maine! Who knew?