Les grottes are 90 caverns with a pull shaft to the surface. There the stones for Carthage were quarried (I don't know whether for the Punic or the Roman).
The stones were later reused in the Medina of Tunis.
They are also installed in the amphitheater of El Jem. A few caverns near the restaurant were once a museum,
e.g. Everything is freely accessible at the moment, things get particularly interesting further up. Take a garbage bag with you, the wind always blows things in!