What was once the world’s largest building in terms of square footage, Chicago’s Merchandise Mart, has made some upgrades designed to get “the tenants to stay in the building longer over the course of the day, and working harder,” said David Greenbaum president of the New York-based Vornado Realty Trust.

Vornado bought the property in 1998, and since then has spent $40 million on renovations to appeal to the tastes of the “millennial” crowd.

“Our building, the Mart, has become the epicenter of what is this extraordinary resurgence of River North in Chicago,” said Greenbaum.

The changes were made to the ground level common spaces of the 86-year-old building which sees over 25,000 people passing through each day. The centerpiece of what’s new is a 50-foot-wide marble staircase which connects the first floor with the second. The 38 steps are designed for hanging out, with enough seating for 200 people between the floors. There is free Wi-Fi and a projection screen also in the open space.

At the top of the staircase visitors will be greeted with a spectacular view of the Chicago River and skyline. Also upstairs there is a new lounge with meeting spaces and a brand new food hall dishing out artisanal wares from local vendors. A food marketplace is in the planning stages, and a 5,000-square-foot green area outdoors will be a relaxing picnic space near the river.

Right now the building is 98 percent occupied. There are 550 tenants, including some big names such as Motorola Mobility, 1871, Yelp, eBay, PayPal and Allstate.

The Merchandise Mart opened in 1930, developed by Marshall Field and Co. With 24 floors and 4.2 million square feet of interior space, the building was the largest until the construction of the Pentagon ten years later. In 1945 Joseph P. Kennedy bought the building for $26 million.  The Kennedy Family sold the property to Vornado Realty in 1998 for between $250 and $300 million.