This place is a cave that is both natural and man-made.  The original part of the cave had two openings - one to sea and one to land.  The Berber tribes then found the place and cut stone wheels from the walls, expanding the cave considerably.

The Cave of Hercules has a bit of notoriety.  On October 23, 1995, British rock group Def Leppard played a concert in the cave (along with concerts in London and Vancouver, Canada), thereby becoming the first rock group to play 3 concerts on 3 continents in 1 day.  The achievement was certified by the Guinness Book of World Records.

It is part of the local legend that Hercules stayed here and slept in this cave.

This is one of the more interesting sites in the Tangier area.

You have to pass through Cape Spartel.  The cave is quite close to the summer palace of King of Morocco.