Mount Nasu and Nasu Highlands
You may want to go to Nikko if you visit Tochigi, but I would like to suggest another place: Nasu. It is not very far from Tokyo, and it is a tourist resort, but not as crowded as Nikko.
Mount Nasu is one of the 100 most famous Japanese mountains. It has five peaks: Sanbonyari-1916m, Chausu (active volcano)-1915m, Asahi-1896m, Minamigatsusan-1776m, and Kuro-oya-1589m. You can enjoy great views from the mountain.
Here are some photos taken from Mount Nasu. A few hours walk is necessary.
Komadome-no-taki falls, in autumn and summer:
1000 Jizo and Sessho-Seki
View of Mount Nasu:
This is Nasu#2
Nasu Highlands area accommodation is a bit pricy, but you can stay in Kuroiso, the closest town to Nasu, as a base.
Chus (http://chus-nasu.com/reservation_en/) is a guest house in Kuroiso for backpackers, couples and families. There is a bus service to the Nasu Highlands area from Kuroiso train station. Once you get to Nasu, you can rent a bike (Japanese only website) or ride on a rope way (Japanese only website) to Mount Nasu.