To the east of Usa Hachimangu, just outside the shrine grounds, is a hill with a torii at its base and overgrown steps leading up.
At the top is a small shrine, O shrine (or Ou or Oh or Oo). It is a sessha of Usa Hachimangu and enshrines Hachiman.
According to the legend, when Hachiman returned in 765 from his journey to Nara for the unveiling of the Great Buddha at Todai-ji he stayed on this mountaintop for 15 years.
Very few people seem to make it up here, but obviously some do as attested by the offering left.