The archaeological site of Göbekli Tepe is a vast complex of stone pillars and rooms that were erected in the Neolithic era. The pillars are up to 20 feet tall and fitted into holes carved out of bedrock. The stone at different parts of the site is decorated with carvings of animals and humanoid figures.
The crux of the mystery of Göbekli Tepe is that we don't really know what the site was used for, but if certain theories are correct, it could drastically change our understanding of the development of human society. As it stands now, the complex already challenges our understanding of hunter-gatherer societies (namely that they had the capabilities to build such a monumental structure). Furthermore, the main excavator, Klaus Schmidt, believes it to be a stone-age sanctuary, a religious site, which pre-dates current ideas of where religion came in the development of society.
Whatever it is, Göbelki Tepe is an absolutely awe-inspiring place.