Have you been to the Temple of the Sea God? Poseidon's temple is located on Cape Sounion, a little less than 50 miles from Athens and it's a great day trip. I've been several times and I never tire of it.
It's an easy place to get to by rental car, KTEL bus or package-trip from your hotel or other tourism sites in Athens. Crowning a low hill over a little inlet, the Doric-style temple was built around 440 B.C. It's apparently THE place to be for sunsets and moonrises, although I've never been fortunate enough to have been there at either time. Below it is a small beach with a hotel and a couple of wonderful seaside tavernas. Your best plan is to either arrive early in the morning when it's a bit cooler and explore the temple, then wander down to cool off at the beach for a swim and have a delicious seafood lunch. Alternately, see the temple at sunset and plan on a moonlit dinner! The point of land it sits on is heavy with legend. In the days of the hero Theseus, the kingdom of Athens was obliged to send tribute to the more powerful kingdom of Crete, and that tribute was seven youths and seven maidens. They would be fed to the monstrous Minotaur who lived in a massive labyrinth. Theseus, son of Aegeus, the king of Athens, offered himself up as tribute one year to try and defeat the Minotaur. The ship that sailed the doomed young people to Crete had a black sail of mourning; King Aegeus told him to hoist a white sail if he should return victorious. As the legend goes, Theseus killed the Minotaur and sailed triumphantly home, but in the excitement of victory, forgot to hoist the white sail. His father the king, who would look out from Sounion each day for Theseus' return, saw the black-sailed ship coming into view, and in his great grief, threw himself off the cliff into the sea. The sea is forever named after him now - the Aegean. The god of the sea, Poseidon, was thought to have been responsible for storms, and a country with almost 8,500 miles of coastline would be keen to placate such a potentially wrathful deity. Ancient people - particularly seafarers - would make offerings at the temple to appease the god. If you have a good zoom lens on your camera, be sure to look for where Lord Byron, a great Philhellene who participated in the War of Independence, carved his name into the marble.