The Corinth Canal is an artificial canal in Greece that connects the Gulf of Corinth in the Ionian Sea with the Saronic Gulf in the Aegean Sea. It cuts through the narrow Isthmus of Corinth and separates the Peloponnese from the Greek mainland, making the peninsula an island. The canal was dug through the Isthmus at sea level and has no locks. It is 6.4 kilometres in length and only 24.6 metres wide at sea level, making it impassable for many modern ships. It is currently of little economic importance and is mainly a tourist attraction.
The canal was initially proposed in classical times and a failed effort was made to build it in the 1st century AD. Construction recommenced in 1881 but was hampered by geological and financial problems that bankrupted the original builders.
Wikipedia https://en.wikipedia.org/wiki/Corinth_Canal
Coordinates 37°56'2.845" N 22°59'4.899" E