The term "mythical fountain" can be replaced with a variety of synonyms to convey a similar meaning. One possible alternative is "legendary spring," which suggests a magical or otherworldly source of water with fantastical powers. "Mystical well" is another possibility, emphasizing the spiritual or supernatural qualities of the water source. "Enchanted waters" is another option, indicating a location imbued with mystique and wonder. "Fabled stream" suggests a waterway that has been the subject of stories and legends. Whatever synonym is chosen, it should express the sense of awe and wonder associated with the idea of a mythical fountain.