Hyaku-do Mairi (百度参り)

Hyaku-do mairi (the hundred-fold visit) is a folk religious practice in Japan, in which a person visits a temple or shrine in order to pray to the gods and then, at that same temple or shrine, pays his or her respects one hundred times. It is also called simply "O-hyaku-do" (hundred-fold).

Summary
In terms of the content of the prayers offered during such hundred-fold visits, in most cases it is a personal prayer specific to the individual; if the content of the prayer is urgent, the wish is that by visiting and paying homage to a shrine or temple many times, instead of just once, the person's heartfelt prayer stands a better chance of coming true.

Originally, people would visit their nearby patron Shinto god or famous shrine or temple every day for a hundred days; this was called the "Hyakunichi mode" (hundred-day visit). This was either simplified or changed due to people having prayers they urgently wanted answered and thus could not wait one hundred days; at any rate, a version in which people visited the shrine or temple one hundred times in a single day came to replace the hundred-day visit. We know from entries in the "Azuma kagami" (Mirror of the East) that hyaku-do mairi was being performed as early as the beginning of the Kamakura period. That is, according to the "Azuma kagami," on September 28, 1189, several groups of ladies-in-waiting to the shogun's wife at the palace went to Tsurugaoka in order to pray for the success of the northward search and destroy mission; or again, on August 21, 1241, the Hojo clan is described as having gone to Tsurugaoka and made a hundred-fold prayer. And according to the "Heikoki," on March 13, 1240, the author performed a hundred-fold visit at Gion Shrine.

How to perform a hundred-fold visit
The method of performing a hundred-fold visit is as follows: go from the entrance to the temple or shrine as far as the main worship hall or main temple building and pay homage, and then return to the entrance of the temple or shrine, and simply repeat this process one hundred times.
In common speech, this is called 'stepping (there) one hundred times.'

Sometimes, near the entrance to the temple or shrine, a stone pillar called a 'hundred-fold rock' is erected to serve as the objective of these circumlocutions. To keep people from losing count, the temple or shrine stacks up one hundred pebbles, twisted paper strings, bamboo skewers or the like, which supplicants take one at a time and place by the main hall, counting by using these hundred pebbles, etc. as a sort of makeshift abacus.

Some claim that hundred-fold visits should be performed without anyone else witnessing them, or that they are more effective if done barefoot.