Did Atlantis really exist?

It must have. There is a Russian guy - PHD, an eye doctor, who took a picture of the eyes that can be found drawn on/in most of the Buddhist temples and ran it through the computer program that builds your appearance based on eyes, then he took this picture with him on expedition to Himalayas and Tibet showing it to Lamas and Swamis. 

They recognized the picture. It was the picture of either Atlantians or Lemurian. Apparently there are samadhi caves in the mountains where those representatives of ancient civilizations reside in the state of samadhi (that state could last thousands and even millions of years) being some kind of genetic pool. They are protected by some kind of bio-energetic shield that we can't enter the cave (you get the symptoms of fear, then headache that gets stronger and stronger as you proceed, and if you ignore these symptoms you just die)- only the specially trained keepers can, and they are the only source of proof as we know it. Apparently many Chinese solders when they were occupying Tibet died this way, trying to enter those caves. 

This Russian guy's last name is Muldashev. Not sure if his books are translated into English even though the guy himself does speak the language. He has a couple of books out and they keep coming as results of his expeditions.

There are other sources that speak of ancient civilizations/races. Those sources are based on a religious rather than scientific knowledge though. We are apparently the fifth civilization. The previous ones were destroyed as the Earth was shifting the axis (with all the consequences - floods, ice ages, appearances and disappearances of the continents and so on). The best representatives of those civilizations were preserved in a genetic pool of the planet, in those samadhi caves that could be a part of Shambala. The monuments such as Pyramids (Egyptian, Mexican, Bermudian), Easter Island, Stonehenge, Mt. Kailash (which looks more like a pyramid than a mountain) and others were build by those ancient civilizations, that were obviously much more advanced than we are,some of the monuments managed to survive those Apocalypses. There is some kind of mathematical /geometrical dependency in the way those are placed around the globe -either being the gates into another dimension or something else - this remains to be uncovered/understood …