Inside JLL's headquarters in Chicago

One of Chicago's biggest office buildings recently added a ton of amenities, like a 16,000 square foot gym and meeting space, with panoramic views of the city.

The Aon Center building now boasts the city's largest amenity space, with a café, games, work space, and more, run by real estate company JLL.

JLL redesigned the lobby, amenity floor, and its own six-floor headquarters within the building.

Before the revamp, JLL spent two years surveying and interviewing the 900 employees who worked in the building. That changed how leadership thought about everything from location to design, the head of JLL's workplace strategy practice told Business Insider.

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Chicago's Aon Center might not win any awards for most interesting building from the outside – the 83-floor office building is one gray, long rectangle that towers over Millennium Park.

Inside, however, recent renovations now allow employees to exercise, play games, host meetings, and sip lattes with panoramic views of the city from the 70th floor. Later this spring, they'll be able to have cocktails there, too.

JLL, the world's second-largest real-estate company, embarked on major upgrades to the building that reshaped common spaces like the lobby and amenities floor, as well as its six-floor headquarters.

See more: We visited the new San Francisco office of $19 billion Atlassian, where every little detail is designed to help people work together

Before reworking its own floors, JLL spent two years surveying and interviewing the firm's 900 local employees, which led to a number of surprises, Ed Nolan, the head of the firm's workplace strategy practice, told Business Insider. For example, the company's leadership assumed most employees commuted in from the suburbs, but the survey found half came in by public transit, ride-sharing services, walking, and biking.

Understanding that the workforce was more urbanized than executives thought led the company to stay in the Aon Center, even though the building is farther from commuter trains connected to the suburbs than many other offices.

Nolan said JLL undertook the renovations with three principles in mind:

Agility: Before the renovations, the office floor plan was 80% assigned – employees had cubicles or offices. Now, only 50% is, with the rest of the floorplan dedicated to shared space, like phone booths and small conference rooms. JLL's headcount grew from 900 to 1,400, but the firm still occupies the same six floors, thanks to a smaller per-employee footprint.

Connection: Employees felt siloed in their previous cubicles or office space, disconnected from the larger company, so the company added a 3,000 square foot lounge. Nolan said it's now common for employees to spend three or four hours working in the club space, rather than at their desks. Two staircases, one in the club and another near reception, are also meant to foster more connection than riding in an elevator.

Choice: Gone are the cubicles, in are options to work at a rolling desk, private room, conference room, lounge, kitchen, and other areas.

We toured the office and amenity center to see how those principles look in action.