The size and scope of the temples, mausoleums, and other buildings of Nikko is astounding. Each site is hidden behind the others, surrounded by massive cedar trees and climbing up into the mountainside. I was somehow unaware until arriving that this was the final resting site of the founder of the Tokugawa Shogunate, which of course lends massive historical importance to the architectural beauty. It's a lovely day trip from Tokyo, but the town itself is also in a beautiful stretch of country, so it's worth coming out and taking the time to enjoy the scenery as well. 

There are generally lots of visitors, both foreign and Japanese, so just be aware of that going in. Bring solid shoes and be prepared for many steps!