I recently traveled to Greece and had taken to cruising Wikipedia for interesting bits of information. I will now relate them to you.
Greece is located at the southern tip of the Balkan Peninsula. Drilling further down, Athens lies on the Attica Peninsula, and to the west Corinth (red pin) sits at the gateway to the larger Peloponnese Peninsula. Pylos and the nearby Costa Navarino resort are located on the southwest coast of the Peloponnese at the Ionian Sea.
Just north of Corinth the peninsula is actually severed from the mainland by the Corinth Canal. This water route through the Isthmus of Corinth was dreamt of for hundreds of years, but when it was finally completed in 1893 it was already obsolete due to the change in maritime practices. It was too narrow and no longer saved time on useful trade routes. Nevertheless, you can see how it cuts the land today and we will need to cross it using one of 5 bridges this summer. The Canal is only 80 feet wide and features a submersible sea-level bridge at either end. Which just seems like a crazy thing to build.
All this means that the Peloponnese is technically now an Island, though like Cape Cod it is still commonly considered a peninsula!