Praying wheels are filled with Tibetan mantras. They come in a wide variety of sizes. From small hand wheels for daily use to large wheels weighing several tons.
They are rotated clockwise, which is believed that the mantras filled inside the praying wheels are being repeated and activated to the sky and show a positive effect. The large heavy prayer wheels usually contains hundreds to millions of mantras.
Likewise, with each rotation of a praying wheel a small bell is struck. It shows that again some millions of mantras are completed.