The site at the top of the mountain contains elaborate rock altars used for sacrifices. From the High Place, one can view much of Petra from above. Beautiful scenery. It can get cold and windy up there. The trek down the back side of the mountain reveals many interesting tombs and carvings that might be missed by the average tourist. The round trip generally takes 1.5-2.5 h. Not many people go through the back route as it's not always clear where it starts - ask or use OpenStreetMap to identify the track. You might even try to use the direct track to the Treasury, which is even harder to find and not official, even though the staircases are clearly visible from down the Treasury.