Bagnaccio is a popular spa resort outside the city limits of Viterbo near the similar village of Bullicame. It consists of three baths, which officially are only open to members. In reality, this is never checked and anyone with a car and enough time to make the trek from Rome can visit.
Bagnaccio Viterbo

The baths are located on a property that is owned by a rich family, who, however, believe that they should remain open to the public. This has been opposed by several Viterbian mayors, of the kind who think that what they don’t enjoy nobody should like, throughout the years: although Bagnaccio is visited by families during the day, it is said to be a meeting place for homosexuals at night.
Nowadays, Bagnaccio is run by a non-profit organisation.
Bagnaccio is located about 8 kilometres north-west of Viterbo. From Rome you take the S2 Cassia in northern direction, then the S7 in the direction of Marta. After that you turn right into the Via del Garinei, a gravel road. An unpleasantly smelling, but reportedly extremely healthy, bath awaits you.