New York City’s subway system is currently the world’s sixth busiest, with 1.6-billion annual passenger rides. This means that old subways cars are constantly being replaced with new ones. You might think that the last stop for these old trains would be at some junkyard, but photographer Stephen Mallon tracked the to their watery graves at the bottom of the Atlantic Ocean, where they basically act as artificial reefs. Continue reading for a rare video look, more pictures and additional information.