Near the Takino'o Shrine is a large boulder wrapped in rope on which expectant mothers place rocks and pray for an easy delivery. Also, maybe women place rocks in order to become expectant mothers. Its history goes back at least 600 years (the Takio Shrine is much older than the nearby and much more famous Toshogu Shrine).
These pebbles (and one yen coin) are placed on top of the "signpost" for the big boulder.