"......it was boiling and puffing as if there were damned souls inside, as if in the ground the irascible mob was constantly grumbling ......." (G.D'Annunzio, "Maybe yes, maybe no", 1910).

In Sasso Pisano it is still possible to see how those places looked like until the end of the 16th century. A hellish –looking valley filled with hot fountains, sulphuric steaming holes, all in all a place easily connected to the Devil by the superstitions of the past, enough to lead some historians to believe that these landscapes gave Dante Alighieri the inspiration that allowed him to write the description of the entrance of Hell as he described it in his Divine Comedy.

Those phenomena are a result of the presence of a magmatic body in a low depth, that enters in contact with the rocks and the water system. Next to these smoky emissions one can easily distinguish the altering of the soil and the rocks connected with the emitted kinds of gas such as carbon dioxide, methane, ammoniac, boric acid and the characteristic sulphuric acid which is responsible for the typical smell of "rotten eggs". One can also note the widely diffused exhalations of hot steam (so-called fumarole), exiting from the numerous holes in the soil as well as small water puddles emanating gas.

In Sasso Pisano one can also note the activity of a small geyser, with a frequency of emission of only a few minutes.

A suggestive path allows the visitor to have a look at the most enjoyable events connecting the two medieval Hamlets of Sasso Pisano and Monterotondo Marittimo.

The many thermal water fountains next to the small Hamlet of Sasso Pisano also feed some old washhouses, among them you can find one which has recently been restored and is located in the proximity of the Cemetery; the second has not be restored and can be found next to the Enel village of the Lagoni di Sasso Pisano.