Sure is a marvel, and dispels some myths of ancient men being overly primitive. 15 foot walls and pillars with inscriptions from the days before the Israelites were enslaved in Egypt. There are a lot of other sites on the same hills which haven’t even been opened yet. We know they are there from ground radar type scans. So one can venture a guess that this site was part of a larger civilization. Maybe ceremonial or maybe multi purpose. Though it does appear it was deliberately buried, too, which makes the mystery all the greater. Maybe they wanted to protect it from marauders or something…
Other sites with remarkable construction tend to show a relatively short burst of creativity, followed by somewhat rapid collapse, as happened on Easter Island. The EI statues date from about 1250 AD to about 1500 AD, and it sez here that nearly half of them were never moved out of the quarry, which implies that the precipitous end to the statue-building phase — as recorded in their folklore — came about in a pretty short time frame near the end of that period.