It is the name of the main fumarole of the Solfatara, where the water steam reaches a temperature of about 160°C. In the inside of this opening some salts contained in the steam, including Realgar (As S), Cinnabar (Hg S) and Orpiment (As2 S3), condense giving a yellow-reddish colour to the surrounding rocks; there is also the emission of Hydrogen Sulphide (H2S), with its characteristic odour of rotten eggs.
The area of the Bocca Grande was called by the ancients Forum Vulcani, i.e. the Dwelling of the God of Fire.
At the beginning of '900 the German volcanologist Friedländer built here a small Volcanological Observatory, of which some ruins still remain, which collapsed, due to the periodic telluric movements connected to both the Bradyseism of the Phlegrean area and the opening of a fumarole.
