Stromboli is a small island created by a volcano which is one of the most active in the world. If you love the adventure you can reach the craters with a skilled local guide and the necessary equipment that you can also rent on the island (resistant shoes, helmet and lamp).
On the craters you can closely observe the volcano eruptions with lava bursts. The return trip including a stop to the crater takes about 4 hours.
You can also stay on your boat at sea and observe the volcano from the flank of the Sciara del fuoco, by keeping the required safety distance.