For my money, there are two "not-to-miss" sights in the overall Kanto area.
One is the look on the face of my dog, Tofu, when I crack open the door on a winter's morning to let her out into a yard covered by a late night snow. Tofu cannot speak of course, but in this instance her expression alone communicates well enough. It says, ". . . Aw, shit."
While that particular sight is priceless, the other costs only 400 yen. That's the entrance fee to a creaky museum just minutes from Nippori Station in north Tokyo, a place I am fairly in love with. So, as a labor of love, let me now crank out some free advertisement for a sightseeing gem that is neither hidden nor unpolished, just mostly unheard of.