Temple of Poseidon

The Temple of Poseidon, the ancient Greek god of the sea, dominates the southernmost tip of Attica, where the horizon meets the Aegean Sea. Perched on the craggy rocks of Cape Sounio, the temple is one of the most impressive ancient temples in Greece, enveloped in myth and history from antiquity until the present day. The unknown architect is probably the same one who built the Temple of Hephaestus in the Ancient Agora of Athens.

source http://www.thisisathens.org/explore/venues-attractions/museums-monuments/museums-monuments/?Id=11