In the ‘flooded’ square of Bagno Vignoni, on the left side from the loggia of Santa Caterina, is the Church of St. John the Baptist.
The ancient parish church, has a single nave, with a very simple facade; inside is preserved a painting of the Sienese school from the sec. 18th century, depicting Saint Catherine of Siena with Bagno Vignoni in the background.
On the porch overlooking the basin is the small chapel dedicated to St. Catherine of Siena erected in 1660. A fresco from the early 17th century depicting the Risen Christ, now detached and preserved in the Church of St. John the Baptist, was placed there.
Every year on June 24, the feast of St. John is celebrated, with a procession around the pool and blessing of the fields. The locality was made famous by St. Catherine Benincasa who often stayed there, in particular, between 1362 and 1367.