The singer and his wife — who celebrated 20 years of marriage last month — hope to leave a lasting legacy with their unique Atlanta mansion

It was love at first sight for Brian and Leighanne Littrell — and their now-18,000 sq. ft. Atlanta mansion.

Months before they tied the knot 20 years ago, the couple moved into the then-5,600 sq. ft. home after falling for its “timeless” feel and glamorous decor.

“We bought it with amazing art and antiques. When we got the keys, it was like, ‘Don’t leave us with the babies!'” jokes Leighanne, 51, an actress who also manages their 17-year-old son Baylee’s country-music career. “It was magnificent, but we were so scared.”

ANDREW HETHERINGTON

ANDREW HETHERINGTON

Since their big move-in day, the Littrells have put their personal touches on every room of the home. From overhauling the kitchen to building out a “wing” for their son, to adding a “playhouse” section of the house, Brian and Leighanne have spared no expense to perfect their dream abode.

ANDREW HETHERINGTON

ANDREW HETHERINGTON

“This place had a certain class, and we’ve tried to make it better in every way we could,” says the Backstreet Boy, 45.

On any given day, “I move stuff around, buy fabric to make curtains … people think I’m crazy sometimes!” adds Leighanne.

On their massive property (which includes a lake), the couple has a sizable guesthouse for visitors, a pool house, an indoor basketball court featuring original flooring from Kentucky’s Rupp Arena and more. With nine bedrooms and 12 bathrooms, there’s no shortage of space for the Littrells and their two dogs Willie and Ellie Sue.

Their favorite rooms are ones where they can hang out as a family, and dad and son can often be found jamming out in the home studio.

ANDREW HETHERINGTON

ANDREW HETHERINGTON

ANDREW HETHERINGTON

“It’s one of the most creative spots,” says Brian. “This is where all the ideas come, and we like to spend time as a family.”

Big entertainers, the Littrells are looking forward to the day when they can safely host friends and family again. But for now, the stars are enjoying some quieter nights at home.

“We make new things old, and we make old things new,” says Brian about their approach to home decor — and marriage.

“With the history of our family being here for so long,” he adds, “it’s a joy to see what you envisioned really come to fruition.”

For all the details on Brian and Leighanne Littrell’s Atlanta home, pick up the latest issue of PEOPLE, on stands now.