Nikkō National Park in Tochigi has so much to see and do that one day is not enough. You could easily spend a whole day just wandering around the historic shrines and temples.
Even though Tōshō-gu is currently being renovated, it is still fabulous. However my second trip to Nikko was by car, and after admiring Suganami-ki, the avenue of 400 year old cedars, we raced through Tōshō-gu, Rinno-ji and Futara-san as soon as they opened. Then we drove to Kegon Falls and Lake Chuzenji.
We continued on to Lake Yunoko and Ryuzu Falls, and for me at least, the natural splendors of Nikkō National Park were a match for the man-made splendors of Tōshō-gu.