Which ancient wonder is the only one whose exact location has never been conclusively proven?

The ancient wonder whose exact location has never been conclusively proven is the Hanging Gardens of Babylon.

The gardens are traditionally said to have stood in Babylon, near present-day Hillah in Iraq, and to have consisted of elevated terraces planted with trees, vines, and other vegetation. Ancient writers described them as an extraordinary feat of engineering, sometimes comparing the terraces to an artificial mountain. A later tradition attributed them to Neo-Babylonian King Nebuchadnezzar II, who ruled from 605 to 562 BC, possibly to comfort his Median queen, Amytis.

The mystery persists because no surviving Babylonian text clearly mentions the gardens, and archaeologists have found no definitive remains at Babylon. Herodotus, who described Babylon, also did not record them. This absence has produced several theories: the gardens may have been a literary invention, they may have existed but vanished, or Greek writers may have confused Babylon with Nineveh.

The Nineveh theory links the story to Assyrian King Sennacherib, who ruled from 704 to 681 BC and built an elaborate irrigation garden near modern Mosul. The other six wonders have more securely identified sites, making the Hanging Gardens the standard answer to this trivia question.