While the golden-topped Dome of the Rock mosque is the most recognizable landmark on the Temple Mount in Jerusalem, the Al Aqsa mosque is the more important of the two structures. In the image I linked to below, the Al Aqsa mosque is on the far left part of the Temple Mount, with the gray dome. The Dome of the Rock mosque sits in the middle.

The Al Aqsa mosque is allegedly where King Solomon's stables were, and also where the Knights Templar's headquarters was while they lived in Jerusalem from 1119-1129 A.D., during which time they excavated underneath the Temple Mount. Rumors abound about what the Templars found in their excavations. Was it gold? Scrolls? The Ark of the Covenant? No one knows for sure. But modern day archaeologists have found material evidence of the Templars' presence underneath the Temple Mount.