>>37142
>Where would prehistoric civilizations be?
Pretty much everywhere. The americas, the atlantic ocean, northern europe, the north pole, antarctica, etc. A lot of cities were built near the coast and were submerged by water after the sea levels rose during the end of the last ice age.
>When would they be?
It's hard to put a specific date on it, but it's safe to say that advanced civilisations existed tens of thousands of years ago. Atlantis almost certainly existed, and it was destroyed 11,600 years ago. This is the date that Plato gave us and it's been confirmed by geological data. There's been a lot of speculation about the dating of the sphinx and the great pyramid of Giza, with estimations based on astronomical calculations going as far as 16k-25k years ago. Tihuanaco is probably around at least 15k years old. According to the Egyptian and Sumerian lists of god kings, their histories go back hundreds of thousands of years.
>How advanced might they have gotten?
The people who ruled over those civilisations (and later, their priests) had access to very advanced science and technology, beyond what we have today (UFO technology). But that knowledge was kept hidden from the masses. The average guy wasn't flying around on his personal spaceship. It's pretty much certain that Egyptians used machine-powered saws to cut some stones, since no other tools could have done it.