Wikipedia
Tenarus
Tenarus was an ancient town of the Peloponnesus, in Laconia (Sparta), on the promontory of Taenarum (modern day Cape Matapan). A cavern near Tenarus was considered the entrance to Hades, through which Heracles dragged Cerberus from the underworld in his 12th labor, and also through which Orpheus led Eurydice back among the living. Through this association the infernal world was often styled "Tenarus" among classicist writers.
Tenarus was famous for a green marble much prized in the ancient world, as well as the purple snail that yielded the prized Lacedaemonian Purple dye. It was also famous for valuable marble , known for its red and black elements.