Zac Efron may have found refuge from his modern-day troubles ... by looking to the ancient past -- namely ... the Incan ruins of Machu Picchu in Peru.
Zac just posted this picture on his Whosay account -- with a big grin on his face as he posed on a mountaintop more than 7,970 feet above sea level.
TMZ broke the story ... Efron was in rehab twice this year for a serious cocaine problem.
Zac said he was in Peru with his dad ... and thanked his fans for all their support.
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