A four-feet granite stone basin in the Eastern passage of Knowth may be engraved with a map of the city of Atlantis, as Plato described it. The three concentric circles match the three concentric lakes of Atlantis.

The similarity was noted by Dr. Ulf Erlingsson, who visited Knowth last month. His book Atlantis from a Geographer's Perspective: Mapping the Fairy Land will be released in Europe September 30 th (16.95). Plato described an inner island 5 stadia in diameter, surrounded by a circular lake 1 stade wide.

Continuing out, there was a circular island and another lake, each 2 stadia wide. Finally there was another island and lake, each 3 stadia wide. A stade equals 100 fathoms, or 200 yards. Dr Erlingsson suggests in his book that the megalithic yard should be used, which translates to a stade of 166 m.

http://www.mythicalireland.com/ancientsites/knowth/atlantis-map-in-knowth.php

Anthony's comment:
There are a lot of concentric circles on stones in the Boyne Valley and further afield. Surely these aren't all maps of Atlantis?