Zac Efron -- Higher Than A Kite In Peru

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.