The Dung Gate is a small gate on the south side of the city. It is the lowest part of the city, and leads down to the City of David, where King David reigned.
This gate was originally not a very large gate, and has been modernized for vehicles to pass through after Jaffa Gate was made inaccessible (by the partition of Jerusalem in 1948). The modernizing took place by the Jordanians in 1953.
Today, it serves as an access point for vehicles traveling to the Western Wall, which is just north of the Dung Gate's position.
The current gate has a small gate to the west, that allows pedestrians a safe entrance and exit from the Western Wall.
Sources Used
The Holy Land. Jerome Murphy-O'Connor.
Genesis 1948. Dan Kurzman.
The New Encyclopedia of Archaeological Excavations in the Holy Land. Israel Exploration Society.