In the region of Peloponnese in Greece there is a small village called Pavlopetri,

…where you can find an ancient city dating back 5,000 years resides. However, this is not an ordinary archaeological site, since the city is about 4 meters underwater.It is actually believed that this underwater city is the oldest known submerged city in the world.
The city is wonderful designed with roads, two store houses with gardens, temples, a cemetery, and a complex water management system including channels & pipes.In the center of the city, there is a square, measuring about 40×20 meters and most of the buildings have been found with up to 12 rooms inside.The design is almost the same with the design of many cities today. The city is so old that it existed in the period that the famed ancient poem ‘Iliad’ was set in.
Scientists estimate that the city was sunk in around 1000 BC due to some catastrophic earthquakes. However, despite this and even after 5,000 years, the arrangement of the city is still clearly visible and at least 15 buildings have been found.

John Henderson of the University of Nottingham, and his team, created an extremely accurate 3D reconstruction of the city.
Historians believe that this city had been a center for commerce for the Minoan Civilization and the Mycenaean civilization, since there are big storage containers made from clay, statues, everyday tools and other artefacts. The name of the city is ‘still unknown.