Among the wonders provided by nature in the Gambassi Terme area, in addition to the large woodland stretches rich with Mediterranean scrub, you can find some thermal springs phenomena, a little over a kilometre away from the hamlet, in the valley floor of the Casciani Torrent.
The I Bollori hypothermal spring can be reached leaving the hamlet of Gambassi and walking along the section of the Via Francigena road which leads from the hamlet to San Gimignano. It is a walk which affords spectacular views of the Valdelsa area, Certaldo and the famous San Gimignano towers. Surrounded by vineyards and centuries-old holm oak woods, right after the Casanova hamlet, you take a path on the right that leads to the valley floor of the Casciani torrent. After passing through Santa Teresa, you reach the San Claudio farm. Continuing along the Casciani you quickly arrive to I Bollori.
The waters that regularly gush out of the subsoil are distinguished by gas outpourings, together with rises of thermal waters, which reach the highest concentration near the hypothermal spring called I Bollori (23° C)
The waters of the spring are classified as sulphate-alkaline clayey, with a predominance of calcium sulphate due to the washing away of deep evaporite rocks. The presence of sulphate is the reason for the characteristic smell. While flowing, because of the drop in temperature and pressure, it deposits calcium carbonate which forms a kind of mud used for therapeutic purposes and in case of skin diseases.
The thermal waters of Gambassi Terme were already known in medieval times, when Gambassi was a stopping place for pilgrims and wayfarers who traveled along the Via Francigena.
The I Bollori spring has been used by the local population, even in the past, for the treatment of dermatological diseases in animals.