The Western Wall is the holiest site in the world for Jews and is all that remains of the Second Temple. When visiting, some pray, some cry, and others leave notes in the cracks. Jerusalem is also holy for Muslims, who have two beautiful mosques, including the Dome of the Rock built in the 7th century. The Biblical Zoo in Jerusalem houses animals mentioned in the Bible and is strictly kosher. Yad Vashem is a Holocaust museum that documents Jewish life before and during the Holocaust and memorializes the 6 million Jews and 1.5 million children murdered by Nazis.