The concert includes songs from Twain's latest compact disc, "UP!" including the singles "I'm Gonna Getcha Good" and "Forever and for Always."
"It's not a touring show," Twain says. "It's more the idea of a one-off. There isn't a dramatic theme or anything like that. It's pretty much a straight-ahead rock summer concert in the park. That's the feeling I want to give off. It's not the same sort of production direction you might take on a stadium tour.
"It's a much freer feeling than that, which is great. I've been off tour for three-and-a-half years. We haven't been on stage for so long, and for me, there's something fresh about it and exciting. There'll be an adrenaline that's higher than usual."
Twain chose Chicago, she says, because "It just ended up being a great location. The city itself is cool, but we had to think about park location. This happened to be a park that is well suited to setting up a big concert.
"The city's been so cooperative. That's been the main reason -- who can we work with that's really going to make this happen? They've been amazing."
As for the kind of faces she expects to see in the crowd, Twain suspects it will be varied. "If I look at my audience, they're so salt-and-peppered. Maybe there'd be a group of six teenage girls, then you'll see, beside them, a family with parents in their 30s and their two kids under eight. Then, you'll see maybe an older couple on the other side.
"It's really funny to see all these people just getting into the music, and how they all react and respond to each other."
Twain feels her mixed crowd will help keep her free concert a positive experience. "They all feed off of each other. It keeps people who would maybe get out of control, more in control, and it pipes everybody else up who might normally prefer to sit at a concert."
These days, Twain balances her music career with the personal commitments of marriage to producer and songwriter Robert John "Mutt" Lange, and being a mom to their toddler son, Eja.
"Mutt was actually more of a musical influence on me before I met him than he is now," Twain says. "He was responsible for so much of the music in my teens: The Cars, Def Leppard, Bryan Adams, AC/DC, Billy Ocean. A big part of why we came together in the first place was because of his love for country music.
"So, it's quite ironic that I was so influenced by his rock background, and he was so influenced by the country background."
While Twain thinks it's too early to tell how motherhood will affect her music, she does say, "In the future, I will be writing from a deeper perspective. I just feel deeper now. My emotions are deeper; my thought processes are deeper."
For now, she'd just like you to tune in on Tuesday. "I'm hosting this concert, which is how I'm seeing it, and everybody's invited."
