"A tunnel entrance (exactly how it sounds)"
The Brooklyn Battery Tunnel entrance in the Fidi is just what Trinity Place turns into as you enter the tunnel. The tunnel connects Manhattan and Brooklyn by going through the east river almost right under Governor's Island. It has been open since 1950 and it is a toll road. It's basically another way of getting to Brooklyn by going under the river instead of using the Manhattan or Williamsburg Bridges. It's not a street you can live on and it's hard to recommend living anywhere near it because traffic is so jammed here all the time. Being that it's a tunnel entrance, there's nothing to do here but drive. It's nice to know there are other options, though, for the people that are scared of bridges.