Yasukuni Shrine
The shrine was founded in 1869 by Emperor Meiji with the aim of comforting and memorializing the spirits of those who had given their lives for the nation in the turbulent times of the Meiji Restoration. The shrine's name, "Yasukuni," is imbued with a wish for the establishment of a peaceful nation.
Yasukuni Shrine is definitely controversial, but putting that aside, it's worth a visit. There's a pond, a sumo ring, and various statues. Some areas are under renovation, but it doesn't really affect your visit. There's also a museum nearby—the ground floor is free to enter, and on the first floor, you can see planes, a stamp exhibition, and a shop.