Hyakudo-ishi
(lit: A hundred times stone)

There is an old custom that when you make a serious wish to a god,
pray one hundred times a day. (Sometimes until your wish come true).

Usually, Hyakudo-ishi is placed in front of the front shrine.
People go between the hyakudo-ishi and front shrine one hundres times
and make a wish in each time.

The way of counting...
Some people make 100 twists of paper and bound them, then each time when you pray and return to the hyakudo-ishi ,fold it.