Athens is primarily surrounded by the Aegean Sea, which lies to the east and south of the city. The Saronic Gulf, a part of the Aegean Sea, is located to the southwest of Athens. Additionally, the city is bordered by several smaller bodies of water, including the Gulf of Elefsina to the northwest. These waterways have historically contributed to Athens' development as a significant maritime and trade hub.
A body of water such as you describe would be the ocean itself.
An island is a body of land completely surrounded by water.
A body of water almost completely surrounded by water is called an ocean. Oceans will often run into each other.
The Mediterranean Sea was the body of water completely surrounded by the Roman Empire.
Antarctica is surrounded by the Southern Ocean.
An island. Or if your really picky, a floating rock.
The Mediterranean Sea was surrounded by the Roman Empire.
A lake is a body of water surrounded by land. Lakes are typically enclosed bodies of water that are not directly connected to the ocean.
moat.
waterfall
Lake.
Peninsula