The construction of the fountain goes back to the first decade of the 6th century b.C.; it stood at the same place as we see it today, just beside the actual route. It is a rectangular construction measuring eight by six and a half meters. It consists of a stone built basin and a system of underground pipes and spouts carved in the rocks, which supplied the fountain with water. A slabs-paved court extends with stone benches in front of the basin; the visitor would reach it via a staircase with a few steps. The fountain had been restored and its shape had changed several times. The best known version is the one described by Pausanias, the ancient traveler and is dated in approximately the 1st century b.C. It is known as “Castalia of the rocks” and is found some 50 meters higher than the fountain of the Archaic period which is called “Kato (“lower”) Castalia. In order to achieve better access to the fountain, the rock around was smoothened both by length and width and it is at this place that the visitors placed their votive offerings to the Nymph Castalia within the niches constructed on this purpose. During the Post-Byzantine period and the Ottoman occupation, the bigger of these niches was transformed to a chapel of Saint John the Baptist. Just below the niches there was a rectangular rock-cut basin, ten meters by length and half meter by width, which received the water of the spring conducted there via a closed pipe. The façade of the fountain had seven bronze spouts, separated from each other by seven rock-cut pillars. A staircase with eight steps led lower, to a stone paved yard with benches for the visitors.
Castalia of the rocks was excavated in 1878 by the Greek archaeologists S. Dragatsis and E. Kastorchis and Lower Castalia was excavated by the Greek archaeologist A. Orlandos. Both fountains have ever since been conserved and restored.