I’m not sure that this photo, taken by Roy Chapman Andrews, is from Gandan Monastery, but the prayer wheel is certainly close in size and design to the one I saw there.

Large prayer wheel
Here is the one I saw.

Large prayer wheel at Gandan Monastery, Sept. 2006
People had written on it with a variety of pens, probably prayers.

Gandan Monastery prayer wheel, close-up
Categories: Mongolia, Mongolian Culture, Travel