Capes Matapan (Tainaron) and Maleas in the Peloponnese are the two most southerly points of mainland Greece. They have been proposed by Galanopoulos & Bacon  as the Pillars of Heracles, when the early Greeks were initially confined to the Aegean Sea and the two promontories were the western limits of their maritime knowledge.
Luciano Chiereghin is an Italian researcher who has a great interest in the history of the Po Valley, both ancient and modern. In his 2007 book Atlantide al Microscopio (Atlantis Under the Microscope) he has the plain of the Valley as the location of Atlantis (=Hyperborea) and specifically the ancient town of Adria. He also proposes that Majorca, Sardinia, Corsica, Sicily, Crete and the Peloponnese constituted the island territories of Atlantis.
However, he is not the only one to link this region with Atlantis, as Morven Robertson published a book in 2015 with a similar theme. Both authors were drawn to the Po Valley by its size and its proximity to the magnificent mountains of the Alps, which protect the plain from the northern winds.
Diego Marin has favourably reviewed Chiereghin’s book(a).
Pavlopetri is the name given to a sunken Greek city off the southern Peloponnese, discovered as recently as 1967. An Anglo-Greek team of archaeologists have dated the remains to between 2800 and 1200 BC and as such are referring to it as the oldest (known) submerged city in the world(a)(b). This dating places it before the time of Plato and so it did not take long for commentators to suggest that it was possibly the inspiration behind aspects of Plato’s Atlantis narrative. However, the number of known submerged cities in the Mediterranean has been numbered at around 200. Every time one is discovered there is usually an attempt made to associate it with Atlantis, which fades when it is realised that it fails to match many of the other descriptive identifiers noted by Plato.
What I find interesting about Pavlopetri is that apparently it is never referred to in any classical Greek literature. Sceptics often claim that the reality of Plato’s Atlantis is undermined by the fact that Plato is the only ancient author to mention it and yet, Pavlopetri, unknown until the last century, does exist without any known written reference!
An October 2011 BBC documentary City Beneath the Waves Pavlopetri revealed that the port city was more extensive than originally thought and that it traded with other Aegean states particularly the Minoans on Crete.