Hiroshima Peace Memorial
Hiroshima Peace Memorial isn't the happiest place to visit in Japan, but it's still something worth visiting if only to pay tribute to the memorial that is Genbaku Dome. It's also commonly called the A-Bomb dome. The entire site stands on exactly the spot where the world's first atomic bomb fell on August 6 towards the end of WW2 in 1945. It's located in the Peace Park and the area is tranquil but sobering. In spring, you'll be able to see cherry blossoms or sakura that make the whole area touchingly beautiful, you'll definitely want to get a photo of these if you've planned your trip to time with their bloom. At first glance you might be surprised that anything remains on the spot, but you will be able to see that concrete remains, with some metal protrusions which survived.
What you'll also notice is that unlike all the other tourist hotspots you might visit in Japan, or even Hiroshima, the area is very much hushed. The Peace Park itself is pretty hard to miss, as it's Hiroshima's main feature. It spreads over 12,000 square metres of where the town used to be prior to the bomb. The Park is now a designated area of remembrance, dedicated to nuclear disarmament. Because it aims to remind travellers about the bomb's terrible impact and aftermath, it can also be quite chilling. If you go there on the anniversary of the bomb you'll be able to take part in the moment of silence that takes place at quarter past 8 in the morning. This is at the Cenotaph that is nearby the Museum, which itself has videos, photos and exhibitions that tell the story of what happened in 1945. The whole area itself is close to the tram stop, so also pretty accessible.