There are two distinct parts of Nikko that you would probably like to see. One is the temple area which is at ground level in Nikko town. There are several temples in the same area (one has the famous three see no evil say no evil monkeys on its face). Visiting them will take a few hours. The other main area is up a long road to a lake that has swan boats and a nearby waterfall - all of these within walking distance of each other. In the lake/waterfall area there are monkeys (be careful not to look them in the eyes or engage aggressively with them).