There are fragments of the 'Atlantis' legend in almost every culture around the world.  This suggests, but does not prove, that the legend is based on a very ancient truth that was known by the forebears of each of these cultures.

Our main source of information on the legendary Atlantis is the written account by the Greek philosopher Plato.  Plato writes about Atlantis as an advanced civilisation that was destroyed in a huge volcanic cataclysm about 11,600 years ago.  The evidence suggests that there was indeed a volcanic cataclysm 11,600 years ago, and that it was this event that triggered the ending of the Pleistocene Ice Age at that time.

From http://www.atlan.org/faq/index.html:

As many myths describe it, the Flood was caused by a giant submarine volcanic explosion that stirred up the seas, sending them over the continents. So, the waters reached up to the summit of the loftiest mountains, killing all life in their way. The colossal volcanic explosion also covered the skies with cinders and evaporated water, so that, it indeed, "rained for 40 days and 40 nights" and the skies were dark and gloomy for a long time. The event occurred some 11,600 years ago, and caused the end of the Pleistocene or, more exactly, of its last glacial episode.

So we can imagine Atlantis was first shaken by the nearby volcanic activity, causing many buildings to collapse, then it was hit by the surge of flood water, causing further destruction and drowning the inhabitants.  The sky turned dark with the cinders thrown up into the air, and as the flood waters receded they revealed a ruin where once had stood the great city of Atlantis.  Then, as the polar ice caps melted, warmed by the volcanic activity, the sea level rose some 100 to 150 meters, and the low-lying ruined Atlantis was lost beneath the waves.

As far as the location of Atlantis is concerned, we must begin by marking out all the areas that are now beneath the sea level, but were then above the sea level.  Atlantis, though known as the 'sunken continent' could not literally have sunk.  It is more realistic to presume that Atlantis was lost beneath the waves as the sea level rose, as has already been explained.  This leaves a vast band of 'Atlantis' all around the globe, and explains why so many cultures remember this event.  Either every culture truly retains an element of the one Atlantian legend, or else they have simply all recounted the ending of this last Ice Age.  Huge areas of land were lost beneath the sea all around the globe at this time, and any number of settlements may have been destroyed.  It is hard to believe in 'Atlantis', knowing that so many civilisations must have been lost at the same time.  The only way to know once and for all will be to find Atlantis.

There are two convincing theories concerning the location of Atlantis. One indicates the South China Sea (between Australia and Asia), and the other indicates Santorin (previously called Thera) in the Eastern Mediterranean.  The former is furthered by the research of Prof. Arysio Nunes dos Santos at http://www.atlan.org, who holds that the South China Sea would be the most plausible location. However, the theory that Atlantis was located in the Eastern Mediterranean is much more likely, as this would allow Atlantis to be between Egypt (where the Africanus Australopithecus evolved) and Iraq/Iran (where the first Caucasians evolved).  This would support the mythological references to Atlantis as a society where these two races learnt to live in harmony, seeing their differences as equal and opposite complimentary polarities.

Although the cataclysm is reported to have wiped out about 70% of all life on Earth, mankind prevailed, and before Atlantis was destroyed much of their knowledge and wisdom had begun to spread.  It is also maintained in legend that the Atlantians foresaw their destruction, and sent messengers out to educate the fledgling civilisations of the world, so that 'Atlantis' would not be truly lost.  It was, according to these legends, from the teachings of these messengers, as well as the spreading of the Atlantian knowledge by word of mouth in myth and legend, that all sciences and religions were first established.

Atlantis is a myth about a place which may or may not have once existed, many thousands of years ago, but Atlantis is more than a myth - it is a dream.  It is a dream about a society that works, one where everyone has their place.  Maybe Atlantis is a myth about a place that once existed, maybe it is a myth about a place that never existed, maybe it is a myth about a place that could exist in the future....

From Terry Pratchett "The Carpet People":

We must go to Ware.  It's where we all began, in a way.  It's where people first realized that there may be a better way of doing things than hitting one another on the head.