If you are lucky, trained and accustomed to high altitudes and trekking, and especially if there is no ongoing eruption, you can enjoy the sight of the inside of the summit craters. Straight away, you will notice the ever-present tall gas columns coming from the summit fumarole fields. Can you see the bottom of the Voragine?
In absolute silence, even without seeing ash clouds rising from the bottom of the craters, you can distinctly see some explosions: these are simply gas bubbles exploding inside the volcanic conduit when they are about to reach the surface. Enjoy the view with respect and without fear.
In addition to the omnipresent odour from the fumaroles of the Etna summit area, when you breathe in the air you will sense that there is very little oxygen. In reality, the quantity of oxygen in the mixture that makes up the air is still the same, but the lower atmospheric pressure here causes the rarefication of the entire air mixture.
Stop, sit down and place your hands on the crater perimeter. You will feel the ground vibrate, caused by the explosions inside the volcanic conduit.