Some 2km up Via Rosini, which becomes Via Solfatara (about 900m north of the metro), the surreal Solfatara crater was known to the Romans as the Forum Vulcani (home of the god of fire). At the far end of the steaming, malodorous crater are the Stufe, in which two ancient grottoes were excavated at the end of the 19th century to create two brick sudatoria (sweat rooms). Guided, 2½-hour evening visits (adult/reduced €15/6) also run regularly; see the website for dates.
