The Temple of Poseidon
Poseidon was the God of the Seas so it just makes sense that his temple just outside of Athens would be on a cliff overlooking the Aegean sea. The temple greatly contrasted with the Parthenon. There was only a few other people there which made it a much more humbling experience.
Sunset next to the temple was probably one of the most beautiful sunsets I have seen. The colors playing off of the ocean were simply magical. I felt as if I was looking out at a painting in front of me.