CHICAGO (CBS) — The iconic Old Post Office building in downtown Chicago is sporting a new look. After decades of disrepair, it’s bright, shiny, and back in business as a huge hub for some top-notch companies thanks to an $800 million makeover.

Built in the 1920s, reborn in 2019; after sitting vacant for decades, one of the city’s most historic properties has been reawakened.

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At three blocks long and nearly 3 million square feet, the massive building straddles the eastern end of the Eisenhower Expressway, serving as a front door of sorts to downtown Chicago for drivers headed in from the West Side and western suburbs.

After three years of renovations, the Old Post Office has been brought into the new age. The renovated building celebrated its grand opening on Monday, showing off its new layout.

The building is set to be home to business offices, like Uber and Walgreens.

The first new tenants begin moving in this month; among them will be Ferrara Candy, which is currently headquartered in Oakbrook Terrace, but first set up shop decades ago about two miles away in Little Italy.

Ferrara will lease 77,000 square feet at the Old Post Office, bringing 400 employees to its new digs.

Developers say more than 75% of the property has committed tenants, bringing nearly 5,000 new jobs to the city. Officials expect 1.4 million square feet of the building to be fully occupied by next June.

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But what’s business without a little pleasure? The building also offers open public spaces, a gym complete with a boxing ring, and even a lounge area with a bar and bocce ball.

Despite modern upgrades, a few relics remain from the early days of the Old Post Office; from manual typewriters in the lobby to the U.S. Postal Service eagle still proudly displayed above the door.

“Superlatives are very easy to use when talking about the Post Office, probably overuse I myself. It’s the largest post office ever built. It’s the largest redevelopment going on in the nation right now. It’s the largest adaptive reuse of a historic structure,” said Brian Whiting, chief executive officer of The Telos Group, the building’s leasing agency.

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Developers aren’t done yet. A new food hall, a four-acre rooftop park, and an extension of the Chicago Riverwalk also are in the works.