Lama temple - Prayer wheel

The Prayer Wheel is used in Tibetan Buddhism to recite the prayer of mantra. The prayer wheel(s) (there are sometimes several in a row) are spinned clockwise with one's right hand so that the mantras listed on it (in Tibetan and Sanskrit -the sacred language-) turn in the right direction. This action is equivalent to the recitation of prayer because it helps spread the "words" in the air.
Mantras are sacred words or phrases whose sounds are used for meditation. The mantra must be pronounced several times to produce its effect (physical or spiritual blessing). Hence the idea of cycle that can be achieved by making a cylinder rotate several times around its axis.