Ryuzu waterfall is a great starting point for several hikes; Senjogahara (to Yumoto Onsen), Takayama and Lake Sai. See the hiking summary page for more information.
There is vegan restaurant in nikko...but, passers by may not even notice the quaint...
At the base of Sasamekura mountain (the nearest hike from the hostel) is a cafe set on the hill overlooking the river.
Open all year for lunch and dinner (until 8:30/8:30). (Think last order 7:30 - 8:00). Super Delicious!