This our oldest observatorium

 The site of Göbekli Tepe:

 (A) Location of Göbekli Tepe

 in southeast Turkey (Upper Mesopotamia).

 (B) Overview of excavated areas,

showing find locations of skull 1 (a)

 skull 2 (b), and skull 3 (c).

 Credit: Erhan Küçük, Göbekli Tepe Archive,

 German Archaeological Institute (DAI).

 (C) Impression of the monumental

 round-oval buildings with their characteristic

 T-shaped monolithic pillars. Credit: Nico Becker,

 Göbekli Tepe Archive, DAI.

We know GöbekliTepe. It has been suggested that the ancient structure, which still contains huge monuments that keep many secrets, was built to worship Sirius, the brightest star in the Great Canine Constellation.

GöbekliTepe, brought Sirius under the horizon in the years around 15000 BC. After reaching the minimum, Sirius started to come closer to the horizon and it became visible again, very low and close to due. south, towards 9300 BC.

Lot of genuine archaeological mysteries surround humanity's oldest known temple. It seems that it was the world's first astronomical observatory. 

Just a handful of the giant circular and oval rooms at Gobekli Tepe have been excavated so far, but surveys show many more are still buried underground at the site. Each of these round rooms is defined by a ring of hulking T-shaped pillars.

Earth's Northern Hemisphere was covered in enormous Ice Age glaciers when a group of hunter-gatherers in southern Turkey began constructing the world’s first known temple. The site, called Gobekli Tepe, was built roughly 12,000 - 15,000 years ago, with some parts appearing to be even older. However, because the ancient temple is so vast and complex, archaeologists have been busy excavating it since its discovery in 1994. Although Pillar 43 remains a mystery. One believes that one thing is clear about the pillars in general: They were built in a T-shape as a kind of stylized human form, like a person without a head. 

But despite all those years of research, they're still working to unravel the site’s biggest mysteries: 

Who built it, and why? 

At 12,000 years old, Gobekli Tepe predated humanity’s oldest known civilizations. Its megalithic temples were cut from rock millennia before the 4,500-year-old pyramids in Egypt, 5,000-year-old Stonehenge in England, or 7,000-year-old Nabta Playa, the oldest known astronomical site. It even seems construction on some parts of Gobekli Tepe might have began as far back as 14,000 or 15,000 years ago.