Dome of the Rock
The Dome of the Rock houses the rock upon which Mohammed is said to have ascended to heaven, coincidentally the same rock upon which Isaac offered up his son to God, to prove his faith. It is also on the site of the Second Temple of Judaism, or, the Temple Mount. The holiness of the site to the three Abrahamic sites is intense, to say the least.
After the Second Temple was destroyed in the Roman years, leaving Jerusalem in Roman and later Byzantine hands, the Temple Mount became an empty site, used alternately as empty space, or as a city dump. According to legend, when the first Muslim conquerors took Jerusalem, they approached the Temple Mount. There, the conqueror Umar I called the Christian Patriarch of the city before him to answer for the derelict state of the holy site. Insisting that such a site, sacred to all three religions, deserved respect, Umar insisted that the Patriarch himself begin cleaning the Mount.
The Dome was built shortly thereafter, first in a primitive, wooden state between 687 and 691 as a placeholder, and in its final spectacular version somewhat later.