World Trade Center, HubThe transit hub was meant to resemble a bird's wings.Courtney Verrill

Nearly 15 years after the terrorist attacks of 9/11, the World Trade Center Transportation Hub is now partially open to the public. It serves as a connection between New Jersey's Port Authority Trans-Hudson (PATH) trains and New York City's subways, and is right next to One World Trade Center.

The design for the station 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 Transportation Hub the most expensive train station ever. Though the main part of the station that connects to the PATH trains — known as the Oculus — will now be open, other parts, such as the retail space, are still under construction.

Take a look inside the $4 billion hub:

View As: One Page Slides