NGARI, May 30  -- Hidden among sandstone hills in remote western Tibet, a stretch of honeycomb-shaped caverns is way beyond the reach of most travelers.

Known as the Donggar and Piyang grottoes, the 1,000-year-old caverns in the Tibet Autonomous Region's Ngari Prefecture hold one of the world's greatest collections of Tibetan Buddhist murals.

Rigzin Wangzhab, 75, has been guarding the site for more than 20 years.