Campi Flegrei in a day

The sulfur smell struck before we exited the Metro Tunnel into Pozoulli...It was quite strong at the train station. We walked up the hill towards Solfatera, and along the way encountered an excavation of Roman ruins right under the street, and then further along realized that the retaining wall and part of modern building walls were actually re-used Roman walls. Talk about remodeling!
We spent a couple of hours wandering around "Volcano Solfatera". Plenty of steam emitting from fumaroles with delicate needles of sulfates along the walls of what appears to be an old tuff ring. Some simmering mud pots and hollow sounding ground on the floor of the crater. The most activity were a set of loud jets escaping at a temperature of 160 C. Yellow and orange suffer and arsenic deposits coated the rocks, pretty impressive really.
Later we walked around Pouzzuli at the waterfront, port and old town. We saw the 100 A.D. Roman amphitheater and the "Temple of Serapis" which at one time was below sea level and then reemerged to its present position above sea level; you can see the holes that had been bored by clams. It looks like 10 to 20 meters of up and down motion. This is apparently due to hydrothermal expansion of water saturated layers in the first 1-4 km below the surface. The Campi Flegrei caldera seems to be pretty active. Indeed, as we left town, there was a good view of Monte Nouvo, so named because the 300 m high cone on the edge Pouzzuli is the result of a 1538 A.D. eruption.