The United States Holocaust Memorial Museum, opened in 1993. I visited soon after it opened. It was quite a visit and I recommend that you take the time to check it out when you are in the nation's capital.
Two things that made a lasting impression on me:
First, how crowded the museum was... and I mean really crowded... and yet the deafening silence present in every room of every exhibit. Yes, I know that museums are by nature quiet, but this was a different quiet. It was an inexplicable quiet.
Second, as Jewish prisoners were being herded to the gas chambers, their shoes, among other things, were confiscated from them. There is an exhibit filled with many of those shoes on both sides of the walkway. Scattered a midst the footwear I could see the shoes of children.
We ask God why he allows such suffering. God asks us why we allow it to happen.