Though specific plans to develop the site of the failed Chicago Spire remain a mystery, designers at the architectural firm Gensler have imagined the high-profile waterfront location as an iconic, mixed-use, mega-tall attraction. Taking top honors in an internal company-wide competition, the concept is known as Gateway Tower. Retaining the same 2,000-foot height as the original Spire design, the Gensler concept trades the twisting whimsicality of Calatrava’s narwhal tusk for more of a Chicago-style aesthetic expressed through structural X-bracing.

The aim of the design was not just to pen a very tall tower, but to explore the untapped mixed-use possibilities of the prominent site. Gensler Principal and Chicago office Design Director Brian Vitale explains, "Our solution was to create an anti-tower, one that was not designed purely as an object to look at but rather one that is engaging at different scales to the entire city, one that would welcome newcomers as it simultaneously embraces locals."

While Mr. Calatrava’s Spire was condominium only, the mixed-use concept presented by Gensler not only opens the space up for the enjoyment of more people, it can also be far more financially lucrative. This trend is already seen in New York’s Empire State Building which today brings in more revenue from its observatory than all of its commercial tenants combined. Chicago’s AON Center, the city’s third tallest building, is also reportedly considering the addition of an observatory for this very reason.

Going beyond a typical sky deck, the Gateway Tower study also took a hard look at how the structure could better engage its surroundings — more specifically DuSable Park, the undeveloped and overgrown lakefront parcel located east of the former Spire site and Lake Shore Drive. While the transformation of the three-acre space into DuSable Park was (and still is) part of the Spire’s city-approved Planned Development, such a park was always going to be somewhat of an isolated island, separated from the rest of Streeterville by Lake Shore Drive.

Gensler’s bold solution to activate DuSable sees dramatic outrigger-like stilts that not only reach east of the Drive, but also house funiculars that would allow visitors to "ride" up and down the tower. While this inverted wishbone layout would be in clear violation of Chicago’s Lakefront Protection ordinance prohibiting private development east of LSD, it is nonetheless an impressive exercise in mixed-use creativity and urban connectivity.

"The tiered public experience starts with access at DuSable Park and uses iconic panoramic gondolas with 180 degree views of the city and the lake to reach the mid-section of the tower," says Sasha Zeljic, a Gensler Principal and Design Director in the firm's Chicago office. "Gateway Tower is more than a super-tall icon — it is a unique platform for public amenities."

For all of the design’s grand ambitions, Gensler is certainly not lacking the engineering chops to pull off such a project should Gateway Tower make the leap from conceptual study to real proposal. The international firm has past experience with mega-tall skyscrapers as it designed the Shanghai Tower which currently occupies the number two position on the list of the planet’s tallest buildings, standing no less than 2073 feet.

Dormant since 2008, the site of the failed 150-floor Spire at 400 N. Lake Shore Drive is now controlled by developer Related Midwest. The firm acquired the land in 2015 and has promised an "architecturally significant" development for the location. So far under Related’s stewardship the site has seen the addition of a new landscaped berm to hide the unsightly foundation hole from its immediate neighbors.

Watch: An Etch-A-Sketch of the Chicago skyline