Made world famous after becoming the setting of the Holy Grail's home in Indiana Jones and the Last Crusade, the Treasury is Petra's most recognizable monument. Its facade soars to 40m, creating an imposing welcome to the main ruins area after visitors have exited the siq.
In Arabic it's called al-Khazneh Pharon (the pharaoh's treasury) thanks to a myth that the urn right at the very top of the facade is filled with gold. Although the Treasury's true purpose has never been unearthed, it's thought to have been built as either a tomb for one of Petra's kings, or as a temple dedicated to one of the Nabataean gods.
If you want to see the ornate facade bathed in sunlight, get here early in the morning.