The design is not that of a "typical" Greek temple. It is not flat, but is built on two levels, due to its position on the side of a hill. If you stand beside the north wall of the Parthenon this is the view of the Erechtheion you would see. The temple housed the cults of two gods: Athena and Poseidon, plus it was believed to contain the graves of two mythical kings, Erechtehos and Kekrops. This was also considered by Athenians to be the spot where Athena and Poseidon had a fight over who was going to be the patron of Athens. Each offered the Athenians a gift. Athena offered the olive tree, representative of the area's agricultural wealth, and Poseidon offered the sea, with its strategic position along the Aegean trade routes. The Athenians, obviously, picked Athena and so the contest was decided.
By far the most famous part of the Erechtheion is what is called "the porch of the maidens." The columns upholding the porch are six finely-sculptured maidens, called caryatids.
Although beautiful, they give the impression that holding up part of a building with their heads is no problem at all. These statues are replicas. Five of the originals are in the Acropolis Museum, and the sixth was swiped by good old Lord Elgin while he was helping himself to the Parthenon Marbles. He apparently tried to remove another one but ran into technical difficulties. He tried to saw it into pieces, but this smashed the statue and he just left the fragments lying there. An attempt was made later to reconstruct it.