The Corinth Canal! it connects Gulf of Corinth with the Aegean Sea, if you can fit through it saves sailing down around the Peloponnese peninsula...major shipping route to Athens. 2000 years in the making it was finally finished in 1893. it is 21m wide and the water is only 8m deep. here is a better photo:

http://en.wikipedia.org/wiki/File:Corinth_Canal_2.jpg