6. The Holland Tunnel is a feat of ventilation

When the Holland Tunnel was being built, automobile exhaust contained carbon monoxide levels that could become poisonous within a tunnel. As such, the tunnel would become the first tunnel in the world to be equipped with a ventilation system, “designed specifically for automobile and truck exhaust fumes,” according to ASCE Metropolitan.

There are a total of four ventilation buildings, which contain 84 fans that push air through the tunnel. There are also 42 blowers and 42 exhausters. When the tunnel opened, the plan was to change the air 42 times an hour, which is about once every 85 seconds, but in practice now, not all the fans operate at the same time. Tunnel ventilation buildings now dot the New York City waterfront edge, becoming some of New York’s mysterious windowless buildings.