Jennifer Aniston and Justin Theroux** headed south of the border to celebrate the holidays.

On Christmas Eve, the engaged actors were photographed sunbathing in Cabo San Lucas, Mexico. The We're the Millers actress showed off her toned abs in a hot pink bikini top, while her shirtless, tattooed fiance revealed his sculpted chest and bulging biceps.

Looking fabulous at 43 doesn't come easily for Aniston, who detailed her diet and fitness routine in the March issue of InStyle. "I work out almost every day, at least five or six days a week," the Friends alum revealed. "I do 40 minutes of cardio: spinning, running, the elliptical, or a combination of all three. Then I do Pilates one day a week, and I do yoga in addition to that, three days a week. I try to mix it up."

Even when she's on vacation, Aniston never misses a workout. "I take eight-pound weights with me whenever I'm staying in a hotel," she told the magazine. "It's always good to do arm exercises when you're watching television or talking on the phone."

Aniston visits Cabo San Lucas quite often: In February 2010, she feted her 41st birthday in the vacation destination with Courteney Cox**, Gerard Butler** and Sheryl Crow**, and nine months later she returned to celebrate Thanksgiving with newly-minted BFF Chelsea Handler.

Theroux -- who first met his bride-to-be when she visited the set of Tropic Thunder in 2007 and reconnected years later while shooting the movie Wanderlust -- proposed to Aniston on Aug. 10, his 41st birthday, in New York City. They have yet to announce a wedding date.

This article originally appeared on Usmagazine.com: Jennifer Aniston Unveils Sexy Bikini Body, Shirtless Justin Theroux Flexes Bulging Biceps: Pictures