As the 3rd largest city in Japan, Nikko City covers a large area about 40km by 40km with elevations ranging from 500m about sea level to 2,500m! The total area of Nikko City is 1,449.87 km² or 559.8 m².
For most tourists, the mountain road of Irohazaka offers great views of the changing colors at various altitudes. Any weekend in October is a good time to see the changing colors in Nikko.
However, for the lower parts of Nikko around the 500m above sea level, you can see great colors into the end of November.
Lower Nikko (World Heritage, Toshogu Shrine, Shinkyo Bridge, Zen Hostel) late October to November
Oku Nikko (Senjogahara/Lake Chuzenji/Mt. Nantai/Lake Yuno/Yumoto Hotspring) *highest elevations* September to October
Northern Nikko (Kinugawa, Lake Ikari, Kawaji Spa, Kawamata Spa, Yunishigawa Spa) October to November