Yad Vashem contains many memorials, including the Childrens' memorial (mentioned above) and the "Valley of the Lost Communities", a huge memorial cut into the side of the hill, with the names of the thousands of Jewish communities from Eastern Europe that were destroyed by the Nazis.
These memorials are very appropriate and striking, but none are as effective as the main hall of rememberance.
It's a large but not huge building, probably about 25 metres square. The walls are made of unhewn stones. The ceiling isn't high, and rises to a slightly higher peak near one corner.
Men are asked to cover their heads, a Jewish sign of respect, on entering (Kurt Waldheim as secretary general of the United Nations famously refused), and move along a wide walkway, raised slightly off the floor, that goes along two walls of the building.
You look into the volume of the building. There's nothing fancy, nothing trendy. A Ner Tamid, an everlasting flame, burns in one corner, in perpetual memory of those who lost their lives. Written on the floor, in large stones, in Hebrew and English, are the names of the Nazi Concentration Camps and Death Camps that were in total responsible for the death of about six million Jews. That's about 75 times the capacity of the Stade de France, the state of the art Soccer stadium built for the World Cup in 1998.
Those who forget the past are condemned to repeat it.