Take a ferry from the island of Kos to Nisyros, about a 30 minute boat trip, to the small island of Nisyros. There exists an active volcano which still spews sulfuric and natural gases and smoke. Younger children and older adults are not recommended to visit this location because of precautions against pulmonary issues that may occur. Nevertheless, it is a unique place because it's the largest crater all over Europe! You are surrounded by mountains on this very hot, smoky and rocky terrain feeling as if you are walking on another planet. The ground is so hot, you must wear older shoes because the soles of your shoes will melt! I read this detail before my trip and was glad I didn't ruin a pair of my favorites! Great day trip if you are staying around some of the surrounding islands. Greece... the land of plenty.