The Gunung Padang megalithic site is a recent controversial find. It is located in Indonesia and was originally thought to be a structure built on top of a hill dated 8,500 B.C. from the artifacts found near the site. As recently as October 2014 a survey determined there is a large structure underneath the surface and carbon dating has determined that below the surface could be as old as 14,500 B.C. You can find more about it here. It may be an ancient pyramid that is much, much older than the Great Pyramids of Giza.
Pyramid or natural hill?
Originally thought to just be a site on top of hill