Castalia, in Greek and Romanmythology was a nymph that Apollo transformed into a fountain at Delphi, at the base of Mt. Parnassos, or at Mt Helicon.
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Castalia could inspire the genius of poetry to those who would drink her waters or just listen at their quiet sound; the sacred water was also used to clean the Delphian temples. Apollo consecrated her to the Muses (Castaliae Musae).