Dating from the 3rd millennium BC, these atmospheric ruins cover a large area leading down to an ancient submerged harbour. Highlights include a street paved with geometrical Roman and Byzantine mosaics, on each side of which are rows of large columns. Look out also for the unusually large public Roman bathhouse from the 2nd or 3rd century AD and a 4th-century rectangular arena that would have held up to 2000 spectators, perhaps to watch some sort of ancient water sport.
A five-minute walk north of the main Al Mina site brings you to the ruins of a 12th-century Crusader cathedral, along with a network of Roman and Byzantine roads. Ask at the main ruins, as it's not always open.