The volcano on the island of Nisyros is the youngest one in Greece. It is an active volcano as are the ones at Methana, on Milos Island and on Santorini Island. Most of Nisyros is mountainous, volcanic and very fertile. The island is composed of volcanic rock formations that were formed by previous volcanic activity. The various rock formations (e.g. basalt) have been used as construction material in various buildings such as the Palaiokastro and the bell tower of the Church of Agios Ioannis Theologos located near Nikia. The island has been formed by lava. The rocks are covered by pyroclastic deposits and volcanic mud. Two possible eruptions occurred several millennia ago, estimated around 25,000 years back. The largest crater of the volcano, named Polivotis, has a diameter of 260m and 30m depth. There are another 5 younger craters in the region, the largest of which is Stefanos with a diameter of 30m and a 30m depth. The valley that surrounds the volcano is 2,400m long and 950m wide.

Arriving back into the port of Nisyros you have the opportunity to visit the town of Mandraki. After a short walk through the narrow streets of blue and white painted houses, you have time for lunch (not included) or some shopping or even visit the famous monastery Panagia Spiliani before embarking the boat at 4:00pm for your return to Kos.