New York City's $4 billion World Trade Center Transportation Hub is finally open to the public - take a look inside

Courtney Verrill

The transit hub was meant to resemble a bird's wings.

Nearly 15 years after the terrorist attacks of 9/11, the World Trade Center Transportation Hub has now partially opened to the public. The hub serves as a connection between New Jersey's PATH trains and New York City's subways, and is located right next to One World Trade Center.

The design for the transportation hub was first revealed in 2004. It was projected to take five years and only $2.2 billion to complete, but after 12 years and many complications, $2.2 billion turned into $4 billion, making the World Trade Center Transportation Hub the most expensive train station ever.

Though the main part of the hub that connects to the PATH trains - known as the Oculus - will now be open, other parts of the hub, such as the retail space, are still under construction.

Take a look inside the $4 billion hub.