"In the fading days of the pharaohs, Heracleion was the gateway to Egypt and a port beyond compare"

Swallowed By The Sea: Ancient Egypt's Greatest Lost City

We all know about Alexandria, one of the greatest cities of the classical world, with its great Library and fabled Lighthouse. But Heracleion? A great port and religious centre at the mouth of the Nile, it was mentioned by the likes of Herodotus, but at some point it vanished, and its location became unknown.