Allegory of the Cave
Plato often invokes, particularly in his dialogues "Phaedo", "Republic" and "Phaedrus", poetic language to illustrate the mode in which the Forms are said to exist. Near the end of the "Phaedo", for example, Plato describes the world of Forms as a pristine region of the physical universe located above the surface of the Earth ("Phd." 109a-111c). In the "Phaedrus" the Forms are in a "place beyond heaven" ("huperouranios topos") ("Phdr." 247c ff); and in the "Republic" the sensible world is contrasted with the intelligible realm ("noēton topon") in the famous Allegory of the Cave.