At the Castalian Spring in the ravine of the Phaedriades at Delphi, all comers to Delphi especially suppliants who came to consult the Oracle stopped to wash their hair. Two fountains fed by the sacred spring survive. The archaic (early 6th century BCE) fountain house has a marble-lined basin surrounded by benches. There is also a Hellenistic or Roman fountain with niches hollowed in the rock to receive votive gifts.

The Castalian Spring predates all of classical Delphi: the archaic guardian of the spring was the serpent or dragon Python, killed by Apollo in its lair beside the spring.

The Castalian Spring became a type for a well of inspiration, partly by confusing it with the spring of Pieris.

A town in the state of Tennessee is named Castalian Springs .