Solfatara, a shallow volcanic crater in Pozzuoli, near Naples, is a hotbed (no pun intended) of geothermal activity. Upon walking into the depression, hemmed round by steep hills, the smell of rotten eggs greets your nose. The stench comes from the clouds of sulphurous steam pouring forth from vents in the rock. The Romans believed that this steam had healing properties, and Solfatara was a popular location for convalescent citizens. Visitors can enter the small dens that essentially served as medicinal saunas, though you brave the odors at your own risk.
Those who have visited Yellowstone National Park will recognize the characteristically bright colors (oranges, yellows, and reds) staining the rocks and earth where the gases escape at very high temperatures (see the picture above). Large pits of gray boiling mud (see below) also abound. What might be most surprising, however, is the extreme heat thrown off by the very soil of the crater. The picture below (lowest) might not look like much, but attend to the small hole scraped into the gravel on the right side. If you were to put your finger into that, you would be at risk for a pretty severe burn. (I know, because it almost happened to me.) Even an inch or two below the surface, the temperature climbs to several hundred degrees Fahrenheit as steam escapes soil. The heat creeps up through the soles of your shoes—it doesn’t help if the sun is beating down, but you really get the sense that you’re in a frying pan, so to speak. If you jump up and down, you feel a drum-like resonance caused by the hollows only a few feet below the surface.
Apparently, Solfatara is also home to its very own thermophile found living in the extreme conditions, Sulfolobus solfataricus.