Last weekend during Open House Chicago, the public got an early look at the totally overhauled and fully refreshed Old Main Post Office — now known simply as the Old Post Office. And in just a few more weeks, the broad-shouldered, 2.5 million-square-foot building will open its doors to the thousands of new office workers expected to commute there each day.

Since being closed by the city in 1996, the Old Post Office has sat vacant between Van Buren and Harrison, just west of the Chicago River. Stepping into the building’s polished Art Deco lobby today, you wouldn’t know just how monumental an undertaking its renovation was. Along the way, there were fires, pie-in-the-sky mega proposals, and even an alleged shakedown by now-disgraced alderman Ed Burke. Finally, its $800 million adaptive reuse at the hands of owner 601W Companies is primed to breathe new life into a once-sleepy corner of downtown, drawing legacy corporations back into the city from surrounding suburbs.

Fully occupied, 12,000 to 14,000 employees are expected to work out of the building, says Brian Whiting, a veteran downtown office broker and president of Telos Group, who’s overseeing leasing. According to Whiting, the complex already has commitments for 75 percent of the building’s rentable spaces. Its high-profile tenants include Walgreens, the Chicago Board Options Exchange, Uber Freight, and Ferrara Candy Company, whose 77,000-square-foot office on the sixth floor is complete and ready for the 400 staffers who will move there from its Oak Brook Terrace HQ.

According to Ferrara CEO Todd Siwak, there’s both a symbolic and practical purpose for relocating from the suburbs.

“This building represented the re-engagement with not only this part of the city, but the finishing element to bringing [downtown Chicago] back to its full glory,” he says. “Being here and being in downtown Chicago is important to us, because we, like all of the other leading companies, needed access to world-class talent.”

Not to be outdone by competing upscale office projects, the Old Post Office is big on perks, featuring 80,000 square feet of amenity space including a bar with billiards and bocce, a no-kidding gym with a boxing ring, and plenty of cushy chairs and couches for after-work mingling. Eventually, a four-acre “rooftop park” will open atop the building

Last summer, the Old Post Office’s sprawling floors were still raw, open spaces awaiting build-outs. And just as the project was ambitious in scale, so too was the pace at which its design and construction teams were tasked with working. In time their success could set a precedent for historic preservation and adaptive reuse in Chicago — especially of this size and scale.

“This project is going to be a catalyst,” says Sheryl Shulze of Gensler, the lead architecture firm for the renovation. “We see so many new buildings going up, but we also see so much of our incredible and rich inventory of existing building stock waiting to be repositioned, whether it’s for office, or hotels, or other uses.”

She adds that there’s more than economic sense to these types of renovations, considering how many adapted buildings borrow themes, finishes, and even names from their forebears.

“People really crave authenticity in terms of the story of what places used to be — [those] unique features that you might not find in a modern-day building.”