The entrance to the Ear of Dionysius as seen from outside.

Nestled in a delightful semi-wild garden with Mediterranean flora mixed with exotic plants, which creates a splendid promenade, this is the only one among the quarries of the archaeological area that is currently open for visits (combined ticket at the entrance of the Archaeological Park).

The cave, a virtual “Gothic cathedral” of dizzying height (23 meters / 75.5 feet), tunnels sinuously into the rock for 65 meters / 213 feet, following the path of an ancient aqueduct. 
The diggers began the excavation, in fact, from the aqueduct, avoiding the rock layers above (which were of a lower quality because of water infiltration) and proceeded to gradually dismantle the floor to an increasingly wide area, until reaching the actual level of the ground. 
This technique had the effect of shaping the cave in the curious form of a “pavilion,” which one can also find in other parts of these quarries as well as in the Quarries of the Capuchins.

One can still easily distinguish on the walls the parallel lines of successive layers of rock that were "peeled away" one after another.  For this operation, the workers made use of wooden wedges, which, when wet and expanded, split the stone in a relatively straight line.

In the cavity resulting from this immense excavation work a curious phenomenon of echoes was created (obviously in a way that was completely unintended), which gave rise to the fanciful legend that the caves were built by Dionysius in order to spy on his prisoners, who spoke with complete freedom not knowing that their whispers were audible, thanks to the play of echoes, on the opposite side of the cave.

Until a few years ago, generations of guides amazed tourists who, from a distance of many meters, could easily hear the sound of a piece of paper being torn, “miraculously” amplified by the echo. Today, in the absence of such guides, visitors themselves have fun attempting to make a sound echo the greatest distance.