However, Superman has actually encountered Circe, learning that she actually exists, although possibly not exactly like the myth.
The original Circe was actually a Kryptonian scientist who invented an Evolution Serum, composed partially of Kryptonite. She evolved many Kryptonians into various animals. It is likely she then traveled to Earth, where she became known to the Greeks. ("The Lady and the Lion")
A descendant of the Kryptonian scientist, a modern Mediterranean woman was also named Circe and still had some of the serum invented by her ancestor, though her Kryptonian powers seemed to have been diluted through generations of inbreeding with Humans. ("The Lady and the Lion")