The 601W Cos. unveiled its long-rumored plans for an observation deck atop Aon Center at a public meeting Monday night, and the developer is going big to compete with the observation decks at Willis Tower and 875 North Michigan Ave.

The $150M plan would capitalize on Aon Center's proximity to Millennium Park and the lakefront by building a two-level observation deck on the building's 82nd and 83rd floors. Visitors would be ferried to the deck in two 1,000-foot-tall, glass-encased, double-decker elevators outside the building's northwest corner.

Thrill-seekers will also have the option of riding the Sky Summit, a gondola on Aon Center's rooftop capable of housing 22 people that would hang over the building's ledge for 30 to 40 seconds.

In addition to bird's-eye views, visitors would have access to an outdoor deck and a virtual reality attraction that would simulate flights around the downtown skyline.

601W Managing Partner Mark Karasick is betting the observation deck will make Aon Center a tourist attraction, and told attendees at Monday night's meeting the deck would generate 2 million visitors, an estimated $220M in new tax revenue and $915M in economic impact over a 20-year period.

If the city and residents sign off on the proposal, 601W expects to have construction completed in 2020. It would make Chicago the second city, along with New York, to have three observation decks. But the project would face competition in Chicago for tourist dollars. Blackstone Group and Equity Office is considering a ledgewalk attraction for its renovations to Willis Tower's Skydeck. The 360 Chicago Observation Deck atop 875 North Michigan Ave. has glass cases that tilt forward, giving visitors a view of the street below.