While it may sound strange at first, Robbie's not bathing in alcohol -- she's drinking it!
"I like to have a beer shower," she tells the magazine, "a nice beer in the shower."
Though Robbie's become quite a fan of the relaxing ritual, she doesn't take credit for it. The self-described insomniac actually learned the trick on the set of Whiskey Tango Foxtrot. "When I did Whiskey Tango Foxtrot, I was saying, 'Oh my God, I can't wait to go home,'" she recalls. "And Tina Fey's costume lady was like, 'Me too. I can't wait to go home and have a beer shower.'"
"She said she drinks an ice-cold beer in a boiling-hot bath or shower, and it made her sleep," Robbie explains. "I was like, 'That sounds perfect!' So now when I get home from work, I have a beer shower or a beer bath if I have time."
"It takes a long time to switch my brain off," Robbie adds of preparing for bed, listing eye masks, sleep music and melatonin as ways she powers down for the night.
But when all else fails, it's a little Harry Potter that helps her get the zzzs.
"I'm a massive Harry Potter nerd, and although I've read the books probably 20 times each, I read Harry Potter before bed and it helps me switch my brain off," she reveals.