To the west of the Erechtheion was a sanctuary dedicated to Pandrosos, one of the three daughters of Cecrops. According to myth, the goddess Athena entrusted the three sisters, Pandrosos, Herse, and Aglauros, with the chest containing the infant Erichthonius, commanding them not to open it. Only Pandrosos obeyed the command, and so Athena appointed her as the nurse of Erichthonius. To honour her, the Athenians built a sanctuary next to the temple of Athena Polias, later known as the Erechtheion.
The Pandroseion, which no longer exists today, was a small sanctuary bordered on the north and west by an Ionic colonnade in a Γ-shape. Access to it was through a small gate on the northern side of the Erechtheion. Here stood the sacred olive tree of Athena, which, according to tradition, the goddess gifted to the Athenians after her dispute with Poseidon for the patronage of the city. From Herodotus and Pausanias, we learn that the Persians burned the sacred tree when they set fire to the Acropolis in 480 BCE, but the olive tree sprouted again the next day.
In the southern part of the open sanctuary, the tomb of the mythical king Cecrops was located, the ancestor of the Athenians and the father of Pandrosos. When the Ancient Temple of Athena Polias was replaced by the Erechtheion in the late 5th century BCE, the tomb was incorporated into the architectural design of the Erechtheion. Thus, a portion of it was found situated beneath the porch of the Caryatids, which by then signified the tomb, effectively serving as its above-ground monument.
Finally, another noteworthy Athenian landmark was located at the Pandroseion: the altar of Zeus Herkeios (protector of the household). Some scholars believe that this cult can be traced back to Mycenaean times and suggest that it took place in the courtyard of the Mycenaean Palace, remnants of which were identified in the area where the Erechtheion was later built.