From the official entrance to the site, a dusty trail leads gently downwards along the Wadi Musa (The Valley of Moses). Situated in small rock outcrops to the left and right of the path are some small Nabataean tombs, carved into the dry rock. Beyond these, walls of sandstone rise steeply on the left, and a narrow cleft reveals the entrance to the Siq, the principal route into Petra itself.
The Nabataeans were expert hydraulic engineers. The walls of the Siq are lined with channels (originally fitted with chamfered clay pipes of efficient design) to carry drinking water to the city, while a dam to the right of the entrance diverted an adjoining stream through a tunnel to prevent it flooding the Siq.
Once inside, the Siq narrows to little more than five metres in width, while the walls tower up hundreds of metres on either side. The floor, originally paved, is now largely covered with soft sand, although evidence of Nabataean construction can still be seen in some places.
The Siq twists and turns, the high walls all but shutting out the early morning sunlight, until abruptly, through a cleft in the rock , the first glimpse of the city of Petra can be seen. Carved out of pale reddish sandstone, ornate pillars supporting a portico surmounted by a central urn and two flanking blocks, jut out from the cliff face ahead. This is the Khazneh.