A thick fog lifts over lover Manhattan as seen from One World Observatory in New York City.

It's finally happening. More than 16 years after the World Trade Center tragedy, a major component of the rebuilt WTC site is getting ready to open.

In early June, 3 World Trade Center will be opening with lead tenants including music streaming firm Spotify and advertising giant GroupM.

It will join 1 and 4 World Trade Center — the two other major buildings on the site — along with 7 World Trade Center on Greenwich Street.

The completion of this phase of the World Trade Center comes as New York's financial district is experiencing a renaissance.

I was at the World Trade Center during the 9/11 tragedy and worked at the NYSE in the immediate years after. Back then, the financial district was filled with vacancies and relatively sparsely populated.

And then, it began to change.

"It's a very different neighborhood than it was in 2001, it's very different than it was even five years ago," Jessica Lappin, the president of Alliance for Downtown New York, told me. "We still have financial firms, but what's been amazing is to see tech, media, advertising firms —companies like Spotify and Group M — move down here as well and really change the face of the workforce and the feel of the neighborhood."