Catherine Zeta-Jones keeps her marriage to Michael Douglas problem-free by spending days alone in a specially-built closet at their home. The Welsh actress wed the veteran Hollywood star in 2000, less than two years after they started dating, and many critics suggested the union would soon fail because of the 25-year age gap. But the couple is still going strong 13 years later, and Zeta-Jones has revealed the secret to their success - she has a live-in wardrobe at their U.S. home where she often spends all day watching TV away from her husband. Zeta-Jones tells British magazine Stella, "We spend a hell of a lot of time together, so we are careful to maintain our space. We recently had an extension built, to house a closet. It's like the (Doctor Who) Tardis - I go in there and never come out. My husband knocks on the door and says, 'Can I come in?'. But I've got a TV in there, and my daughter brings her friends in - they play shop, put on all my stuff. I could be in there for the whole day, happily." The Chicago star also reveals she has a novel use for designer high heels that are too precious to scuff on the streets - they are employed as bookends on her shelves. She adds, "I buy shoes sometimes and use them as bookends. They're too beautiful to wear."