The Fonte Anticolana is Fiuggi's second spring, named after the town's original medieval name, Anticoli di Campagna. It sits in a separate section of the spa park from the Bonifacio VIII spring, connected by a pleasant shaded walkway. The water here has a slightly different mineral composition — higher in lithium — which the spa literature will tell you makes it better suited for certain complaints, though both springs draw from the same general aquifer.
In practice, most visitors try both and report they taste much the same. The Anticolana setting is a touch less grand than the main spring, which makes it feel less touristy and more like the locals' preferred option. Worth the short walk from the Bonifacio VIII source to see the full scope of the park.