But it's his current venture, & Juliet, that he describes as "the most wonderful musical that's ever been".

Mills stars as Shakespeare in the jukebox musical which turns the story of Romeo and Juliet on its head, exploring what would happen if Juliet didn't die at the end of the famed play.

Some of the biggest hits of the past three decades - from such artists as Britney Spears, Jon Bon Jovi, The Weeknd and more - help propel the plot.

Producer and songwriter Max Martin is the man behind the hits, while the humorous script comes courtesy of Emmy-winning writer David West Read, of hit comedy series Schitt's Creek.

"I've been a part of six or seven big musicals over the last 15 years, 20 years since Australian Idol, and I've got to say this is the best thing I've ever been a part of," Mills said.

"The story of love, friendship, second chances, joy."

Mills was in Wollongong on Tuesday to promote the show and had praise to heap on the city too, having enjoyed a coffee watching the sunrise over the ocean and a "beautiful" breakfast at CBD cafe Bull and bear.

"It's gorgeous... not as crazy busy, you've got the mountains, you've got the beaches," Mills said.

Next time he hopes to catch a Dragons versus Melbourne Storm game (the Victorian capital is his hometown) at WIN Stadium.

While Mills cannot speak highly enough about & Juliet, he wasn't initially convinced it would work - but when he read the script and heard the music, he thought it was perfect.

The cast also features fellow Australian Idol contestant Casey Donovan and stars Indigenous woman Lorinda May Merrypor in her debut lead role.

While the musical is billed as a party, Mills describes a show that also speaks to deeper themes.

He said he expected it would spark conversations between couples thanks to the on-stage relationship between Shakespeare and wife Anne Hathaway (played by real-life friend Amy Lehpamer), and invite people to consider giving second chances.

Mills is now in the show's final Australian run at Sydney's Lyric Theatre, where the cast delivers eight high-energy shows a week.

Keeping up with the demands of this schedule means Mills devotes his downtime to ensuring he is primed to give his best on stage, from eating well to exercise.

"I'm a strong believer - and it sounds cliche - but it's always going to be someone's first time in the theatre," he said.

"It's going to be the first time that they see something, so put on the very best show so they have a lasting memory of that first-time experience."

With & Juliet playing for another two months, Mills said seeing the show was an opportunity to have faith in humanity restored at a time when there was so much tragedy in the world, having had a friend describe it as pure joy and escapism.

"I think what good art does is allow you to feel the things you didn't know you needed to feel," he said.

"And this show just does it in spades, whether it's come for a really good laugh, because there's so much comedy throughout it [or] come to feel connected with other people around you... this is the one that will do it for you."

& Juliet is playing at Sydney Lyric Theatre until June 16.