The Siq a dramatic and awe-inspiring natural rock formation that works as the main entrance to the ancient Nabatean city of Petra. Also known as Siqit, the main entrance in Petra is a dim, narrow gorge (in some points no more than 3 metres wide) winds its way approximately 1.2 kilometres and ends at Petra's most elaborate ruin, Al Khazneh (the Treasury). A wide valley outside leading to the Siq is known as the Bab as-Sīq (Gateway to the Siq).

Unlike slot canyons like Antelope Canyon, which are directly shaped by water, the Siq is a natural geological fault split apart by tectonic forces; only later was it worn smooth by water. The walls that enclose the Siq stand between 91–182 metres (299–597 ft) in height.

At the beginning of the Siq, one can still view the remains of the city’s gate. On both sides of the Siq, there are channels to draw water from Wadi Musa (the Valley of Moses), from outside the city to the inside.