The teardrop shape of the Ear of Dionysus cavern (Orecchio di Dionisio in the original Italian) is famous for acoustic properties that amplify even the quietest of sounds, allowing them to be heard through an opening at the top, some 72 feet from the ground.

In 1829, journalist and geographer Conrad Malt-Brun observed: "The tearing of a piece of paper makes a noise not unlike that occasioned by knocking a heavy stick against a stone."

The cave, which is characterized by a narrow tunnel at the top that widens into the more expansive cavern below, is believed to have been hewn from an ancient limestone quarry. Some, however, speculate that the unique shape was formed from natural rather than manmade processes and is preserved in its original state due to reverence for the strange acoustics which were perceived as sacred.

The cave was named by Italian painter Caravaggio after the Greek tyrant Dionysius I who ruled Syracuse from 432 to 367 B.C. According to legend, Dionysius used the cave as a prison, spying on his captives from the small opening at the top of the cave where even whispers from the cavern below could be clearly heard. Recent investigations, however, have found this myth to be implausible; though the amplifying effects of the cave's shape are indeed impressive, they don't account for the resonance which garbles even the best enunciated speech. Another more gruesome tale holds that the sadistic emperor, rather than listening for secrets, took satisfaction in hearing the amplified screams of his prisoners as they were tortured.

At one point visitors could ascend to the top of the cave via a rope and pulley in order to fully appreciate the cave's acoustic qualities, but due to safety concerns that option no longer exists and tourists must content themselves with appreciating the effects from the cavern's floor.