spinning and chanting

When the young nun led me somewhere to pray, I had expected a proper temple. Instead, yet another cave temple (though much lower than the rest), with three monks in the semi-light. At first, I couldn't see them, only hear their drone. And whirring. They spun their prayer wheels the fastest I've ever seen, whilst murmuring their chants. The pages are Buddhist scriptures, chanted, then flipped over to chant yet some more.