Koyasan is worth visiting at any time of year, but each season has a distinct character. Spring brings cherry blossoms in late April, when the contrast of pink against ancient grey stone is particularly striking. Summer is cool compared to Osaka and Kyoto — the mountain sits at 900 metres and temperatures rarely exceed 28°C, making it a genuine refuge from the lowland heat. Autumn is the most popular season: the maples turn crimson and orange in late October and early November, and the light filtering through coloured leaves into the Okunoin cemetery is extraordinary. Winter brings heavy snow, which closes some of the smaller temples but transforms the mountain into something austere and otherworldly; the Okunoin lanterns glowing under snow at night is one of Japan's less-photographed scenes.
The major festivals are Rokuji-ko (mid-January), Aoi Matsuri (May), and the O-Bon season in August, when lantern offerings are floated on the small ponds near Okunoin. Weekdays are significantly less crowded than weekends throughout the year. Avoid Golden Week (late April to early May) if possible — Koyasan handles crowds less gracefully than larger cities.