If you are in Oku Nikko, you will surely visit Chuzenji lake and the beatiful area that surrounds it.
Ryuzu Falls is one famous spot, and while you are there you should stop by Ryuzu no Chaya.
This small restaurant offers soba, udon, ramen, yuba, tempura and also delicious dango (sweet Japanese rice dumplings). What makes this place special is the amazing view of Ryuzu Falls, so make sure to be there early to get a good seat!
English menu available, and also a shop to take a look and buy beautiful souveniers before leaving.
Address: 2485 Chūgūshi, Nikko
Website (only in Japanese): http://www.nikko-ryuzu.jp/freepage_9_1.html