• The $25 billion Hudson Yards megadevelopment had its grand opening on March 15.
  • The entire 28-acre project is set to be completed in 2024.
  • While some buildings are still under construction, the site's signaturelandmark a 150-foot-tall honeycomb structure called Vessel is now open to the public.

At $25 billion, Hudson Yards is the most expensive real-estate development in US history. It's also one of the largest, at more than 18 million square feet, including 14 acres of public space.

With many buildings already completed and a few more underway, the development now overwhelms the Chelsea and Hell's Kitchen neighborhoods near the Eastern and Western Rail Yards. Though the project has a recognizable public landmark a 150-foot-tall honeycomb structure known as Vessel its buildings are masterful achievements in their own right.

Read more: Firefighters are warning that lives could be at risk in New York's $25 billion megadevelopment

Business Insider got a peek inside the development site, which was bustling with activity a few months ahead of the grand opening on March 15. Every day there's a new path to navigate, said Geoff Butler, the senior project manager at Related Companies, which is developing the site with Oxford Properties Group.

Even on a cloudy day, the buildings' reflective panels glisten in a celebration of progress.

Take a look at how the development is coming along:

When you step onto the construction site, your eye immediately goes toward Vessel, a $200 million public art installation.

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The structure is the brainchild of Thomas Heatherwick, the British designer behind the 2012 Olympics cauldron and the Seed Cathedral in the UK.

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Vessel consists of 154 interconnecting flights of stairs totaling 2,500 steps.

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The base alone is 50 feet tall.

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The building's 80 landings offer multiple views of the Hudson River.

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The walls consist of a painted steel frame polished with a copper-colored steel skin.

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Construction on Vessel began in April 2017and is scheduled to be complete by March 2019.

Nestled between 10 and 30 Hudson Yards, the site's 720,000-square-foot retail building is anchored by Neiman Marcus, which occupies three floors.

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The building, which is now open, features two gilded observation decks that overlook the public square.

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The building's tenants include Zara, H&M, Sephora, Banana Republic, and Watches of Switzerland, which has a 6,000-square-foot showroom.

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To the right of the retail center is 10 Hudson Yards, which feeds directly into the High Line elevated park. The structure is designed to meet LEED Platinum standards, the highest green-building certification.

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The structure, which opened in May 2016, contains companies like L'Oral USA, Sidewalk Labs, Guardian Life Insurance, and The Boston Consulting Group.

Each year, the site's irrigation systems will filter and reuse nearly 10 million gallons of storm water collected from roofs and public plazas.

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The site uses data sensors to capture traffic patterns, air quality, pedestrian flow, and power demands.

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Before it approved the development plans, the city mandated the construction of a nonprofit cultural center. This led to the creation of The Shed, which will host events like art installations, concerts, and conventions.

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The Shed features a retractable outer shell, which can be activated within five minutes via wireless remote to create a temperature-controlled space.

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The shell is held up by six track-bound wheels that allow it to roll back for outdoor events.

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The building, which drew inspiration from the Palais-Royal in Paris, is being touted as a potential site for New York Fashion Week.

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To the right of The Shed, 15 Hudson Yards offers nearly 300 rental and for-sale residences, including 100 affordable apartments.

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The building which contains a 75-foot swimming pool, a screening room, a rooftop lounge, and a private coworking space directly overlooks the Hudson River.

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A standard apartment starts at about $3.9 million, and at least 60% of the units have already been sold.

The president of Related Hudson Yards, Jay Cross, described the typical tenant as a domestic buyer with multiple homes. He said that perhaps "they've raised their family in New Jersey or Westchester, and they want to have a place in the city."

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Cross called the site "one giant 80/20," a reference to the city's housing program that requires at least 20% of a new building's units to be set aside for lower-income residents.

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Across the plaza is 35 Hudson Yards, the home of a 60,000-square-foot Equinox fitness center and an Equinox Hotel with more than 200 rooms.

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At 1,000 feet tall, the building is the site's tallest residential structure. It includes more than 140 for-sale condos.

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The prism-like structure was designed by David Childs, the architect behind the Freedom Tower.

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Next door is 55 Hudson Yards, a 1.3-million-square-foot tower that's in talks with Apple about leasing office space.

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The entire site features more than 28,000 plants, including a forest of trees that sits above a ventilation system powered by 15 large fans, which help remove the heat generated by the train equipment below.

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The finished project will include two platforms that form a bridge above the Long Island Rail Road tracks. The platforms will eventually cover three-quarters of the Eastern and Western Rail Yards.

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The grand opening marks the public debut of phase one. The second of two phrases is set to be complete by 2024.

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Cross said the goal "is to move the center of gravity" in New York City. Once it's finished, the site is expected to contribute nearly $19 billion annually to the city's economy.

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SEE ALSO: New York's $25 billion megadevelopment can withstand a superstorm or terrorist attack even if the entire city shuts down