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:

The transportation hub has connections to 11 New York City subway lines and the underground PATH trains that connect New York and New Jersey.

The hub was designed by architect Santiago Calatrava, who has worked on buildings in Spain, Switzerland, and Canada. He is currently designing St. Nicholas Church in Liberty Park, another building that was destroyed during the 9/11 attacks.

The Port Authority gave Calatrava the green light to start building the hub in 2005. The exterior is unique, with a wing-like rib structure meant to resemble a bird taking flight. The first pieces of the ribs were installed in 2008, a year before the original projected opening.

The original design meant for the wings of the hub to open and close — much like the Milwaukee Art Museum, which Calatrava also built — but troubles with the budget forced the authority to keep the wings from moving.

The skylight at the top is retractable.

The 330-foot retractable skylight will be open on days accompanied by nice weather, as well as annually on 9/11. One World Trade Center is visible through the skylight.

The glass roof is meant to bring in natural light to the expected 100,000 commuters who will travel through it.

Although there are no stores in the hub at the moment, there are plans to open up many popular retail spaces in August.

It’s projected to have up to 125 tenants, including popular brands like Apple, H&M, Michael Kors, and Victoria’s Secret.

Parts of the hub are still under construction and will open in phases.

The hub opened to the public on March 3. There was an opening ceremony that attracted TV networks, tourists, and locals.

Calatrava was there, too.

People swarmed around the world-renowned architect.

The World Trade Center Transportation Hub is a monument and remembrance of all those who lost their lives on 9/11.

Source: NYC’s B WTC transportation hub is finally open to the public