However, it has now been revealed as the work of artist David Sudler, 58, who lives with his wife in a nearby high-rise.
Sudler said he regularly clears ice from area sidewalks and the idea for the igloo was born when he grew tired of merely stacking the sheets of ice and snow.
"I'm tired of seeing people do face plants," he told DNAinfo.
"A lot of times we've got hundreds of people walking down the sidewalks and they aren't done properly," Sudler told WLS-TV. "So, I come and do the corners and I thought, 'Well, what the hay. Let's have some fun.'"
Sudler said he was amused by the reactions of passersby.
"I like doing things that make people say, 'Ooooo, how did that happen? Where did that come from?' " Sudler told Red Eye Chicago.
The city has yet to declare whether or not it will allow Sudler's igloo to last until it melts, but the artist said he has a goal before the structure is demolished.
"I'll probably sleep in it one night. I'm sure I will," Sudler told WFLD-TV.
